Fahrenheit, Celsius & Kelvin
Last reviewed: May 2026
Convert between the three major temperature scales: Fahrenheit (daily use in the U.S.), Celsius (scientific and international standard), and Kelvin (absolute scale for physics and chemistry). The formulas are simple but easy to mix up — this converter handles them instantly.1
| Description | °F | °C | K |
|---|---|---|---|
| Absolute zero | -459.67 | -273.15 | 0 |
| Water freezes | 32 | 0 | 273.15 |
| Room temperature | 68–72 | 20–22 | 293–295 |
| Body temperature | 98.6 | 37 | 310.15 |
| Water boils | 212 | 100 | 373.15 |
| From → To | Formula |
|---|---|
| F → C | (F − 32) × 5/9 |
| C → F | (C × 9/5) + 32 |
| C → K | C + 273.15 |
| K → C | K − 273.15 |
Three temperature scales are in common use. Fahrenheit (°F): Water freezes at 32°F and boils at 212°F. Used in the U.S., Bahamas, Cayman Islands, and Palau for weather and cooking. Celsius (°C): Water freezes at 0°C and boils at 100°C. Used everywhere else and in all scientific contexts. Kelvin (K): Absolute scale starting at absolute zero (0 K = −273.15°C). Used in physics and chemistry. No degree symbol — it's just "300 Kelvin," not "300 degrees Kelvin."
°F to °C: subtract 32, multiply by 5/9. °C to °F: multiply by 9/5, add 32. °C to K: add 273.15. Quick mental shortcut: for °F to °C, subtract 30 and divide by 2 (rough approximation — 72°F ≈ 21°C, actual is 22.2°C). The two scales intersect at −40° — the only temperature that reads the same in both. Some useful reference points: body temperature is 98.6°F = 37°C, room temperature is roughly 68-72°F = 20-22°C, and a hot summer day of 95°F = 35°C.
Meat safety temperatures (USDA): Poultry: 165°F (74°C). Ground beef: 160°F (71°C). Pork, beef steaks, fish: 145°F (63°C) with 3-minute rest. Oven benchmarks: Low/slow: 250-300°F (120-150°C). Moderate: 350°F (177°C). Hot: 400-425°F (204-218°C). Broil: 500°F+ (260°C+). Candy stages: Soft ball: 235-240°F (113-116°C). Hard ball: 250-266°F (121-130°C). Hard crack: 300-310°F (149-154°C). An instant-read thermometer ($10-15) is the single most useful kitchen tool for food safety and cooking precision.
Normal body temperature averages 98.6°F (37°C), but that number is more of a guideline than a rule — it varies by person, time of day, and where you measure. Oral readings range from 97.6-99.6°F normally. Fever thresholds: 100.4°F (38°C) for adults, 100.4°F for children (per the AAP). Hypothermia begins below 95°F (35°C). Heatstroke occurs when core temperature exceeds 104°F (40°C). Temporal artery (forehead) and tympanic (ear) thermometers read 0.5-1°F higher than oral; rectal readings are 0.5-1°F higher than oral. When reporting temperature to a doctor, always specify the measurement method.
Hottest air temperature recorded: 134°F (56.7°C) in Death Valley, 1913. Coldest: −128.6°F (−89.2°C) in Antarctica, 1983. Sun's surface: 9,941°F (5,505°C). Liquid nitrogen: −321°F (−196°C). Tungsten melting point: 6,192°F (3,422°C) — highest of any pure metal. Steel forging: 1,800-2,300°F (982-1,260°C). Superconductors operate near absolute zero, typically below −420°F (−252°C). These extremes illustrate why Kelvin is preferred in science — it avoids negative numbers for most physical processes.
Each temperature scale reflects its creator's practical priorities. Daniel Fahrenheit (1724) calibrated his scale using three reference points: 0°F was the coldest he could achieve with an ice-salt mixture, 32°F was the freezing point of water, and 96°F was human body temperature (later refined to 98.6°F). Anders Celsius (1742) took the simpler approach: 0° for water's freezing point and 100° for boiling (originally reversed, with 0° as boiling). Lord Kelvin (1848) created the absolute scale starting at absolute zero — the theoretical point where all molecular motion stops — making the Kelvin scale essential for physics and chemistry since negative temperatures have no physical meaning in thermodynamics. The conversion formulas connect these: °F = °C × 9/5 + 32, °C = (°F - 32) × 5/9, and K = °C + 273.15. A useful shortcut: -40° is the same in both Fahrenheit and Celsius — the only point where the two scales intersect.
Cooking temperatures illustrate why precise conversion matters. The Maillard reaction — the chemical browning that creates flavor on seared steaks, toasted bread, and roasted coffee — begins around 280°F (138°C) and accelerates above 330°F (165°C). Caramelization of sugars starts at 320°F (160°C). Deep frying operates at 350-375°F (177-191°C) — below 325°F food absorbs oil and becomes greasy; above 400°F oil begins to break down and smoke. Food safety temperatures are critical: the USDA danger zone (40-140°F, 4-60°C) is where bacteria multiply rapidly. Chicken must reach 165°F (74°C) internally, ground beef 160°F (71°C), and whole cuts of beef and pork 145°F (63°C) with a 3-minute rest. European recipes specify oven temperatures in Celsius: 180°C = 356°F, 200°C = 392°F, 220°C = 428°F. British recipes sometimes use gas marks, where Gas Mark 4 = 350°F = 177°C and each mark represents roughly 25°F (14°C).
The practical range of temperature extends far beyond everyday experience. Liquid nitrogen boils at -320°F (-196°C, 77 K), used in cryopreservation, flash-freezing food, and removing warts. Dry ice sublimates at -109°F (-78.5°C). The coldest place on Earth, Vostok Station in Antarctica, recorded -128.6°F (-89.2°C) in 1983. At the other extreme, iron melts at 2,800°F (1,538°C), glass softens at 1,000-1,500°F (538-816°C), and the surface of the Sun reaches 9,941°F (5,505°C). Laboratory settings reach even greater extremes: the Large Hadron Collider produced temperatures over 7 trillion °F (4 trillion °C) — hotter than the center of the Sun — while laser cooling experiments have achieved temperatures within billionths of a degree of absolute zero. At these extremes, Fahrenheit and Celsius are impractical; scientists use Kelvin exclusively because proportional relationships in thermodynamics (doubling temperature doubles thermal energy) only work correctly on an absolute scale.
Actual air temperature doesn't always reflect what your body experiences. Wind chill describes how cold air feels when wind accelerates heat loss from exposed skin: 20°F (-6.7°C) with 25 mph wind feels like 3°F (-16°C), because moving air strips the insulating boundary layer of warm air around your body. Frostbite becomes possible within 30 minutes at wind chills below 0°F and within 10 minutes below -20°F. The heat index works in reverse: high humidity prevents sweat from evaporating, reducing your body's cooling efficiency. At 90°F (32°C) with 70% humidity, the heat index reaches 106°F (41°C) — heat stroke risk territory. Both indices are calculated using complex formulas (the NWS wind chill formula has 4 terms including wind speed raised to the 0.16 power) and are reported in the same unit as the ambient temperature, which can confuse people who don't realize "feels like" is a calculated value, not a measured temperature.
The exact formula (°F = °C × 1.8 + 32) is inconvenient for mental math. Quick approximations: double the Celsius value and add 30 for a rough Fahrenheit estimate — 25°C ≈ 2(25)+30 = 80°F (actual: 77°F, close enough for weather). Key benchmarks worth memorizing: 0°C = 32°F (freezing), 10°C = 50°F (cool), 20°C = 68°F (room), 30°C = 86°F (hot), 37°C = 98.6°F (body), 100°C = 212°F (boiling). For precision, each 5°C change equals exactly 9°F — so starting from any memorized benchmark, just add or subtract 9°F for each 5°C step. From body temperature (37°C = 98.6°F): a fever of 39°C is 2°C higher, or roughly 3.6°F higher = 102.2°F. These mental shortcuts make international weather reports, European thermostats, and metric recipes immediately interpretable without pulling out a calculator.
Each temperature scale reflects its creator's practical priorities. Daniel Fahrenheit (1724) calibrated his scale using three reference points: 0°F was the coldest he could achieve with an ice-salt mixture, 32°F was the freezing point of water, and 96°F was human body temperature (later refined to 98.6°F). Anders Celsius (1742) took the simpler approach: 0° for water's freezing point and 100° for boiling (originally reversed, with 0° as boiling). Lord Kelvin (1848) created the absolute scale starting at absolute zero — the theoretical point where all molecular motion stops — making the Kelvin scale essential for physics and chemistry since negative temperatures have no physical meaning in thermodynamics. The conversion formulas connect these: °F = °C × 9/5 + 32, °C = (°F - 32) × 5/9, and K = °C + 273.15. A useful shortcut: -40° is the same in both Fahrenheit and Celsius — the only point where the two scales intersect.
Cooking temperatures illustrate why precise conversion matters. The Maillard reaction — the chemical browning that creates flavor on seared steaks, toasted bread, and roasted coffee — begins around 280°F (138°C) and accelerates above 330°F (165°C). Caramelization of sugars starts at 320°F (160°C). Deep frying operates at 350-375°F (177-191°C) — below 325°F food absorbs oil and becomes greasy; above 400°F oil begins to break down and smoke. Food safety temperatures are critical: the USDA danger zone (40-140°F, 4-60°C) is where bacteria multiply rapidly. Chicken must reach 165°F (74°C) internally, ground beef 160°F (71°C), and whole cuts of beef and pork 145°F (63°C) with a 3-minute rest. European recipes specify oven temperatures in Celsius: 180°C = 356°F, 200°C = 392°F, 220°C = 428°F. British recipes sometimes use gas marks, where Gas Mark 4 = 350°F = 177°C and each mark represents roughly 25°F (14°C).
The practical range of temperature extends far beyond everyday experience. Liquid nitrogen boils at -320°F (-196°C, 77 K), used in cryopreservation, flash-freezing food, and removing warts. Dry ice sublimates at -109°F (-78.5°C). The coldest place on Earth, Vostok Station in Antarctica, recorded -128.6°F (-89.2°C) in 1983. At the other extreme, iron melts at 2,800°F (1,538°C), glass softens at 1,000-1,500°F (538-816°C), and the surface of the Sun reaches 9,941°F (5,505°C). Laboratory settings reach even greater extremes: the Large Hadron Collider produced temperatures over 7 trillion °F (4 trillion °C) — hotter than the center of the Sun — while laser cooling experiments have achieved temperatures within billionths of a degree of absolute zero. At these extremes, Fahrenheit and Celsius are impractical; scientists use Kelvin exclusively because proportional relationships in thermodynamics (doubling temperature doubles thermal energy) only work correctly on an absolute scale.
Actual air temperature doesn't always reflect what your body experiences. Wind chill describes how cold air feels when wind accelerates heat loss from exposed skin: 20°F (-6.7°C) with 25 mph wind feels like 3°F (-16°C), because moving air strips the insulating boundary layer of warm air around your body. Frostbite becomes possible within 30 minutes at wind chills below 0°F and within 10 minutes below -20°F. The heat index works in reverse: high humidity prevents sweat from evaporating, reducing your body's cooling efficiency. At 90°F (32°C) with 70% humidity, the heat index reaches 106°F (41°C) — heat stroke risk territory. Both indices are calculated using complex formulas (the NWS wind chill formula has 4 terms including wind speed raised to the 0.16 power) and are reported in the same unit as the ambient temperature, which can confuse people who don't realize "feels like" is a calculated value, not a measured temperature.
The exact formula (°F = °C × 1.8 + 32) is inconvenient for mental math. Quick approximations: double the Celsius value and add 30 for a rough Fahrenheit estimate — 25°C ≈ 2(25)+30 = 80°F (actual: 77°F, close enough for weather). Key benchmarks worth memorizing: 0°C = 32°F (freezing), 10°C = 50°F (cool), 20°C = 68°F (room), 30°C = 86°F (hot), 37°C = 98.6°F (body), 100°C = 212°F (boiling). For precision, each 5°C change equals exactly 9°F — so starting from any memorized benchmark, just add or subtract 9°F for each 5°C step. From body temperature (37°C = 98.6°F): a fever of 39°C is 2°C higher, or roughly 3.6°F higher = 102.2°F. These mental shortcuts make international weather reports, European thermostats, and metric recipes immediately interpretable without pulling out a calculator.
Each temperature scale reflects its creator's practical priorities. Daniel Fahrenheit (1724) calibrated his scale using three reference points: 0°F was the coldest he could achieve with an ice-salt mixture, 32°F was the freezing point of water, and 96°F was human body temperature (later refined to 98.6°F). Anders Celsius (1742) took the simpler approach: 0° for water's freezing point and 100° for boiling (originally reversed, with 0° as boiling). Lord Kelvin (1848) created the absolute scale starting at absolute zero — the theoretical point where all molecular motion stops — making the Kelvin scale essential for physics and chemistry since negative temperatures have no physical meaning in thermodynamics. The conversion formulas connect these: °F = °C × 9/5 + 32, °C = (°F - 32) × 5/9, and K = °C + 273.15. A useful shortcut: -40° is the same in both Fahrenheit and Celsius — the only point where the two scales intersect.
Cooking temperatures illustrate why precise conversion matters. The Maillard reaction — the chemical browning that creates flavor on seared steaks, toasted bread, and roasted coffee — begins around 280°F (138°C) and accelerates above 330°F (165°C). Caramelization of sugars starts at 320°F (160°C). Deep frying operates at 350-375°F (177-191°C) — below 325°F food absorbs oil and becomes greasy; above 400°F oil begins to break down and smoke. Food safety temperatures are critical: the USDA danger zone (40-140°F, 4-60°C) is where bacteria multiply rapidly. Chicken must reach 165°F (74°C) internally, ground beef 160°F (71°C), and whole cuts of beef and pork 145°F (63°C) with a 3-minute rest. European recipes specify oven temperatures in Celsius: 180°C = 356°F, 200°C = 392°F, 220°C = 428°F. British recipes sometimes use gas marks, where Gas Mark 4 = 350°F = 177°C and each mark represents roughly 25°F (14°C).
The practical range of temperature extends far beyond everyday experience. Liquid nitrogen boils at -320°F (-196°C, 77 K), used in cryopreservation, flash-freezing food, and removing warts. Dry ice sublimates at -109°F (-78.5°C). The coldest place on Earth, Vostok Station in Antarctica, recorded -128.6°F (-89.2°C) in 1983. At the other extreme, iron melts at 2,800°F (1,538°C), glass softens at 1,000-1,500°F (538-816°C), and the surface of the Sun reaches 9,941°F (5,505°C). Laboratory settings reach even greater extremes: the Large Hadron Collider produced temperatures over 7 trillion °F (4 trillion °C) — hotter than the center of the Sun — while laser cooling experiments have achieved temperatures within billionths of a degree of absolute zero. At these extremes, Fahrenheit and Celsius are impractical; scientists use Kelvin exclusively because proportional relationships in thermodynamics (doubling temperature doubles thermal energy) only work correctly on an absolute scale.
Actual air temperature doesn't always reflect what your body experiences. Wind chill describes how cold air feels when wind accelerates heat loss from exposed skin: 20°F (-6.7°C) with 25 mph wind feels like 3°F (-16°C), because moving air strips the insulating boundary layer of warm air around your body. Frostbite becomes possible within 30 minutes at wind chills below 0°F and within 10 minutes below -20°F. The heat index works in reverse: high humidity prevents sweat from evaporating, reducing your body's cooling efficiency. At 90°F (32°C) with 70% humidity, the heat index reaches 106°F (41°C) — heat stroke risk territory. Both indices are calculated using complex formulas (the NWS wind chill formula has 4 terms including wind speed raised to the 0.16 power) and are reported in the same unit as the ambient temperature, which can confuse people who don't realize "feels like" is a calculated value, not a measured temperature.
The exact formula (°F = °C × 1.8 + 32) is inconvenient for mental math. Quick approximations: double the Celsius value and add 30 for a rough Fahrenheit estimate — 25°C ≈ 2(25)+30 = 80°F (actual: 77°F, close enough for weather). Key benchmarks worth memorizing: 0°C = 32°F (freezing), 10°C = 50°F (cool), 20°C = 68°F (room), 30°C = 86°F (hot), 37°C = 98.6°F (body), 100°C = 212°F (boiling). For precision, each 5°C change equals exactly 9°F — so starting from any memorized benchmark, just add or subtract 9°F for each 5°C step. From body temperature (37°C = 98.6°F): a fever of 39°C is 2°C higher, or roughly 3.6°F higher = 102.2°F. These mental shortcuts make international weather reports, European thermostats, and metric recipes immediately interpretable without pulling out a calculator.
Each temperature scale reflects its creator's practical priorities. Daniel Fahrenheit (1724) calibrated his scale using three reference points: 0°F was the coldest he could achieve with an ice-salt mixture, 32°F was the freezing point of water, and 96°F was human body temperature (later refined to 98.6°F). Anders Celsius (1742) took the simpler approach: 0° for water's freezing point and 100° for boiling (originally reversed, with 0° as boiling). Lord Kelvin (1848) created the absolute scale starting at absolute zero — the theoretical point where all molecular motion stops — making the Kelvin scale essential for physics and chemistry since negative temperatures have no physical meaning in thermodynamics. The conversion formulas connect these: °F = °C × 9/5 + 32, °C = (°F - 32) × 5/9, and K = °C + 273.15. A useful shortcut: -40° is the same in both Fahrenheit and Celsius — the only point where the two scales intersect.
Cooking temperatures illustrate why precise conversion matters. The Maillard reaction — the chemical browning that creates flavor on seared steaks, toasted bread, and roasted coffee — begins around 280°F (138°C) and accelerates above 330°F (165°C). Caramelization of sugars starts at 320°F (160°C). Deep frying operates at 350-375°F (177-191°C) — below 325°F food absorbs oil and becomes greasy; above 400°F oil begins to break down and smoke. Food safety temperatures are critical: the USDA danger zone (40-140°F, 4-60°C) is where bacteria multiply rapidly. Chicken must reach 165°F (74°C) internally, ground beef 160°F (71°C), and whole cuts of beef and pork 145°F (63°C) with a 3-minute rest. European recipes specify oven temperatures in Celsius: 180°C = 356°F, 200°C = 392°F, 220°C = 428°F. British recipes sometimes use gas marks, where Gas Mark 4 = 350°F = 177°C and each mark represents roughly 25°F (14°C).
The practical range of temperature extends far beyond everyday experience. Liquid nitrogen boils at -320°F (-196°C, 77 K), used in cryopreservation, flash-freezing food, and removing warts. Dry ice sublimates at -109°F (-78.5°C). The coldest place on Earth, Vostok Station in Antarctica, recorded -128.6°F (-89.2°C) in 1983. At the other extreme, iron melts at 2,800°F (1,538°C), glass softens at 1,000-1,500°F (538-816°C), and the surface of the Sun reaches 9,941°F (5,505°C). Laboratory settings reach even greater extremes: the Large Hadron Collider produced temperatures over 7 trillion °F (4 trillion °C) — hotter than the center of the Sun — while laser cooling experiments have achieved temperatures within billionths of a degree of absolute zero. At these extremes, Fahrenheit and Celsius are impractical; scientists use Kelvin exclusively because proportional relationships in thermodynamics (doubling temperature doubles thermal energy) only work correctly on an absolute scale.
Actual air temperature doesn't always reflect what your body experiences. Wind chill describes how cold air feels when wind accelerates heat loss from exposed skin: 20°F (-6.7°C) with 25 mph wind feels like 3°F (-16°C), because moving air strips the insulating boundary layer of warm air around your body. Frostbite becomes possible within 30 minutes at wind chills below 0°F and within 10 minutes below -20°F. The heat index works in reverse: high humidity prevents sweat from evaporating, reducing your body's cooling efficiency. At 90°F (32°C) with 70% humidity, the heat index reaches 106°F (41°C) — heat stroke risk territory. Both indices are calculated using complex formulas (the NWS wind chill formula has 4 terms including wind speed raised to the 0.16 power) and are reported in the same unit as the ambient temperature, which can confuse people who don't realize "feels like" is a calculated value, not a measured temperature.
The exact formula (°F = °C × 1.8 + 32) is inconvenient for mental math. Quick approximations: double the Celsius value and add 30 for a rough Fahrenheit estimate — 25°C ≈ 2(25)+30 = 80°F (actual: 77°F, close enough for weather). Key benchmarks worth memorizing: 0°C = 32°F (freezing), 10°C = 50°F (cool), 20°C = 68°F (room), 30°C = 86°F (hot), 37°C = 98.6°F (body), 100°C = 212°F (boiling). For precision, each 5°C change equals exactly 9°F — so starting from any memorized benchmark, just add or subtract 9°F for each 5°C step. From body temperature (37°C = 98.6°F): a fever of 39°C is 2°C higher, or roughly 3.6°F higher = 102.2°F. These mental shortcuts make international weather reports, European thermostats, and metric recipes immediately interpretable without pulling out a calculator.
Each temperature scale reflects its creator's practical priorities. Daniel Fahrenheit (1724) calibrated his scale using three reference points: 0°F was the coldest he could achieve with an ice-salt mixture, 32°F was the freezing point of water, and 96°F was human body temperature (later refined to 98.6°F). Anders Celsius (1742) took the simpler approach: 0° for water's freezing point and 100° for boiling (originally reversed, with 0° as boiling). Lord Kelvin (1848) created the absolute scale starting at absolute zero — the theoretical point where all molecular motion stops — making the Kelvin scale essential for physics and chemistry since negative temperatures have no physical meaning in thermodynamics. The conversion formulas connect these: °F = °C × 9/5 + 32, °C = (°F - 32) × 5/9, and K = °C + 273.15. A useful shortcut: -40° is the same in both Fahrenheit and Celsius — the only point where the two scales intersect.
Cooking temperatures illustrate why precise conversion matters. The Maillard reaction — the chemical browning that creates flavor on seared steaks, toasted bread, and roasted coffee — begins around 280°F (138°C) and accelerates above 330°F (165°C). Caramelization of sugars starts at 320°F (160°C). Deep frying operates at 350-375°F (177-191°C) — below 325°F food absorbs oil and becomes greasy; above 400°F oil begins to break down and smoke. Food safety temperatures are critical: the USDA danger zone (40-140°F, 4-60°C) is where bacteria multiply rapidly. Chicken must reach 165°F (74°C) internally, ground beef 160°F (71°C), and whole cuts of beef and pork 145°F (63°C) with a 3-minute rest. European recipes specify oven temperatures in Celsius: 180°C = 356°F, 200°C = 392°F, 220°C = 428°F. British recipes sometimes use gas marks, where Gas Mark 4 = 350°F = 177°C and each mark represents roughly 25°F (14°C).
The practical range of temperature extends far beyond everyday experience. Liquid nitrogen boils at -320°F (-196°C, 77 K), used in cryopreservation, flash-freezing food, and removing warts. Dry ice sublimates at -109°F (-78.5°C). The coldest place on Earth, Vostok Station in Antarctica, recorded -128.6°F (-89.2°C) in 1983. At the other extreme, iron melts at 2,800°F (1,538°C), glass softens at 1,000-1,500°F (538-816°C), and the surface of the Sun reaches 9,941°F (5,505°C). Laboratory settings reach even greater extremes: the Large Hadron Collider produced temperatures over 7 trillion °F (4 trillion °C) — hotter than the center of the Sun — while laser cooling experiments have achieved temperatures within billionths of a degree of absolute zero. At these extremes, Fahrenheit and Celsius are impractical; scientists use Kelvin exclusively because proportional relationships in thermodynamics (doubling temperature doubles thermal energy) only work correctly on an absolute scale.
Actual air temperature doesn't always reflect what your body experiences. Wind chill describes how cold air feels when wind accelerates heat loss from exposed skin: 20°F (-6.7°C) with 25 mph wind feels like 3°F (-16°C), because moving air strips the insulating boundary layer of warm air around your body. Frostbite becomes possible within 30 minutes at wind chills below 0°F and within 10 minutes below -20°F. The heat index works in reverse: high humidity prevents sweat from evaporating, reducing your body's cooling efficiency. At 90°F (32°C) with 70% humidity, the heat index reaches 106°F (41°C) — heat stroke risk territory. Both indices are calculated using complex formulas (the NWS wind chill formula has 4 terms including wind speed raised to the 0.16 power) and are reported in the same unit as the ambient temperature, which can confuse people who don't realize "feels like" is a calculated value, not a measured temperature.
The exact formula (°F = °C × 1.8 + 32) is inconvenient for mental math. Quick approximations: double the Celsius value and add 30 for a rough Fahrenheit estimate — 25°C ≈ 2(25)+30 = 80°F (actual: 77°F, close enough for weather). Key benchmarks worth memorizing: 0°C = 32°F (freezing), 10°C = 50°F (cool), 20°C = 68°F (room), 30°C = 86°F (hot), 37°C = 98.6°F (body), 100°C = 212°F (boiling). For precision, each 5°C change equals exactly 9°F — so starting from any memorized benchmark, just add or subtract 9°F for each 5°C step. From body temperature (37°C = 98.6°F): a fever of 39°C is 2°C higher, or roughly 3.6°F higher = 102.2°F. These mental shortcuts make international weather reports, European thermostats, and metric recipes immediately interpretable without pulling out a calculator.
→ Quick F→C estimate: Subtract 30, divide by 2. Close enough for weather.
→ Remember key points: 32°F=0°C, 212°F=100°C, 72°F=22°C.
→ Use Kelvin for science. Never negative, starts at absolute zero.
→ -40 trick: −40 is the same in both F and C.
See also: Length · Weight · Volume · Speed