Pounds ↔ Kilograms ↔ Stone
Last reviewed: January 2026
A body weight converter translates weight measurements between pounds, kilograms, stones, and other units instantly. It is useful for international travelers, athletes tracking training in different unit systems, and anyone reading health information from other countries.
The United States is one of only three countries that primarily uses pounds for body weight, while the vast majority of the world uses kilograms. The conversion is 1 kilogram = 2.20462 pounds.[1] The United Kingdom uniquely uses stone (1 stone = 14 pounds = 6.35 kg) as a common unit for body weight in everyday conversation, even though the metric system is officially used in medical settings.[2] Medical records, drug dosing, and clinical research universally use kilograms, making accurate conversion essential when communicating with healthcare providers across borders.[3] Use the Weight Converter for general weight unit conversions beyond body weight.
See also: BMI Calculator · Height Converter · Ideal Weight Calculator
| Pounds (lb) | Kilograms (kg) | Stone (st) | BMI (5'9" / 175cm) |
|---|---|---|---|
| 120 | 54.4 | 8 st 8 lb | 17.7 |
| 150 | 68.0 | 10 st 10 lb | 22.1 |
| 175 | 79.4 | 12 st 7 lb | 25.8 |
| 200 | 90.7 | 14 st 4 lb | 29.5 |
| 250 | 113.4 | 17 st 12 lb | 36.9 |
Body weight can be expressed in several measurement systems, each with distinct historical origins and regional usage patterns. The metric system uses kilograms (kg) and grams (g) as its primary units, with one kilogram defined as exactly 1,000 grams. The Imperial/US customary system uses pounds (lb) and ounces (oz), with one pound equal to 16 ounces. The stone, still commonly used in the United Kingdom and Ireland for body weight, equals 14 pounds. Understanding conversions between these systems is essential for international travel, medical contexts, fitness tracking, and interpreting health research published in different countries.
The fundamental conversion factor is 1 kilogram = 2.20462 pounds (or equivalently, 1 pound = 0.453592 kilograms). From this base conversion, all other weight relationships can be derived. One stone equals 6.35029 kilograms, and one kilogram equals approximately 0.157473 stones. In medical contexts, body weight in kilograms is essential because drug dosages, BMI calculations, body surface area formulas, and metabolic equations all use metric units. Even in countries that primarily use Imperial measurements, healthcare systems increasingly record weight in kilograms for consistency with international medical literature and drug dosing protocols.
The medical community worldwide standardized on kilograms for body weight to reduce medication dosing errors. When weight is recorded in pounds and must be converted to kilograms for drug calculations, the additional conversion step introduces an opportunity for error. Several documented medication overdose cases have resulted from pounds being entered where kilograms were expected, resulting in approximately 2.2 times the intended dose. The Institute for Safe Medication Practices (ISMP) and the Joint Commission recommend recording all patient weights in kilograms to eliminate this risk.
Drug dosing, particularly in pediatrics and oncology, is frequently calculated as milligrams per kilogram of body weight (mg/kg). Anesthesiology uses body weight in kilograms for calculating drug doses, fluid requirements, and ventilator settings. Nutritional science uses kilograms for calculating Basal Metabolic Rate (BMR), Resting Energy Expenditure (REE), and macronutrient requirements. Research studies universally report body weight in kilograms, and meta-analyses combining data from multiple countries require consistent units. Even fitness applications that display weight in pounds typically perform background calculations in metric units.
Body weight fluctuates naturally by 2-6 pounds (1-3 kg) within a single day, and understanding these fluctuations prevents unnecessary anxiety when tracking weight. The primary drivers of short-term weight changes are water retention and gut contents — not fat gain or loss. Sodium intake causes water retention (each gram of excess sodium can temporarily hold approximately 200 mL of extra water). Carbohydrate intake affects glycogen stores, with each gram of glycogen binding approximately 3-4 grams of water — this is why low-carb diets produce rapid initial weight loss that is primarily water, not fat.
Hydration status, bowel regularity, hormonal cycles (women can retain 2-8 pounds of water during the premenstrual phase), exercise-induced inflammation (muscle repair involves temporary water retention), time of day (you weigh least in the morning after using the bathroom), and even altitude and weather affect scale readings. For meaningful weight trend tracking, experts recommend weighing at the same time daily (first thing in the morning, after bathroom, before eating) and using a 7-day rolling average rather than comparing individual daily measurements. Our Calorie Deficit Calculator helps set appropriate targets for intentional weight changes.
Weight measurement systems have ancient origins reflecting the practical needs of trade, agriculture, and governance. The grain — the weight of a single grain of barley — was one of the earliest standardized units, adopted across multiple civilizations because barley grains are remarkably uniform in mass. The Roman libra (approximately 328.9 grams) gave us the abbreviation "lb" for pound, while the word "pound" derives from the Latin "pondus" meaning weight. The avoirdupois pound (453.59 grams), used for general commerce, became the standard in English-speaking countries, while the troy pound (373.24 grams) remained in use for precious metals and gemstones.
The metric system, developed during the French Revolution in the 1790s, was designed to replace the chaotic patchwork of local measurement systems with a rational, decimal-based standard. The kilogram was originally defined as the mass of one liter of water at 4°C — an elegant definition linking mass to volume. In 2019, the kilogram was redefined in terms of the Planck constant, a fundamental physical constant, making it the last SI base unit to be based on a physical artifact rather than a universal constant. Today, only three countries — the United States, Myanmar, and Liberia — have not officially adopted the metric system as their primary measurement standard, though metric units are used extensively in science, medicine, and international commerce even in these countries.
Body weight alone provides limited information about health status. Two people at the same weight can have vastly different body compositions — one might have 15% body fat and significant muscle mass, while the other might have 35% body fat with minimal muscle. Body Mass Index (BMI), which adjusts weight for height, provides a rough population-level screening tool but fails to account for body composition, bone density, age, sex, and ethnic differences in body fat distribution. Waist circumference, waist-to-hip ratio, body fat percentage, and cardiorespiratory fitness are better individual-level indicators of metabolic health risk than weight or BMI alone. Athletes, particularly those in strength and power sports, routinely have BMI values in the "overweight" or "obese" range while maintaining excellent metabolic health and low body fat percentages. For a more comprehensive assessment, explore our Body Type Calculator and Waist-to-Hip Ratio Calculator.
Weight class sports — boxing, wrestling, martial arts, weightlifting, and powerlifting — require precise weight conversions because governing bodies may use different units depending on the competition level and location. Olympic weightlifting uses kilograms exclusively, while boxing uses pounds in the United States and kilograms internationally. Athletes competing internationally must understand both systems and their exact conversion to make weight successfully. Even small conversion errors can mean the difference between competing in the correct weight class and being disqualified.
See also: Weight Converter · BMI Calculator · Ideal Weight Calculator · KG to LBS
→ Key conversion factors to memorize. 1 kg = 2.205 lbs. 1 stone = 14 lbs = 6.35 kg. For quick mental math: divide pounds by 2.2 to get kg (150 lbs ÷ 2.2 ≈ 68 kg). Multiply kg by 2.2 for pounds.
→ Medical dosing always uses kilograms. If a doctor or pharmacist asks your weight for medication dosing, they need kilograms. Hospital scales typically display both units. For children's medication, even small weight errors affect doses. See our Medication Dosage Calculator.
→ Stone is used primarily in the UK and Ireland. Saying "I weigh 11 stone 3" means 11 × 14 + 3 = 157 lbs (71.2 kg). It's rarely used in medical or scientific contexts but remains common in everyday British conversation.
→ Weight fluctuates 2–5 lbs daily. Water retention, food in your digestive tract, and glycogen stores cause normal daily swings. Weigh yourself at the same time (ideally morning, after bathroom, before eating) and track the weekly average, not individual readings. Use our Weight Converter for non-body-weight conversions.
See also: Weight Converter · KG to LBS · BMI Calculator · Unit Converter