A handful of round numbers from federal agencies shape everyday decisions at home: what counts as one drink, how big an air purifier should be, how humid a basement can get, and how much water a family uses. Each rests on assumptions worth knowing before you rely on it.
| Rule of thumb | Where it comes from | What it assumes | Where it breaks | Calculator |
|---|---|---|---|---|
| 1 drink = 14 g of alcohol | NIAAA’s U.S. standard drink | 12 oz of 5% beer, 5 oz of 12% wine, 1.5 oz of 40% spirits | Craft beer, big wine pours, cocktails; other countries use 8-10 g units | Standard drink calculator |
| Air cleaner CADR about 2/3 of floor area | EPA’s sizing chart (65 cfm for 100 sq ft up to 390 cfm for 600 sq ft) | 8-foot ceilings, one closed room | High ceilings, open floor plans, wildfire smoke, a unit run on low | Air purifier size calculator |
| Indoor humidity 30-50%, under 60% | EPA mold and moisture guide | Measured with a hygrometer, steady conditions | Basements, cold walls and closets can be wetter than the room reading | Dehumidifier size calculator |
| 300 gallons a day, 70% indoors | EPA WaterSense national average for a family | A typical household and climate | Dry Western yards, large families, leaks, efficient homes | Water usage calculator |
NIAAA defines a U.S. standard drink as 14 grams (0.6 fl oz) of pure alcohol (page updated December 2025). It is a unit for counting alcohol, not a description of what people pour. A 16-ounce pint of 7.5% IPA holds 2.0 standard drinks; a 9-ounce glass of 14% wine holds 2.1. Other countries use smaller units (10 grams in Australia, 8 in the UK), so their “units” are not the same thing. The guidance attached to the unit also changed: the 2025-2030 Dietary Guidelines, released in January 2026, dropped the earlier limits of 2 drinks a day for men and 1 for women and advise drinking less for better health, a change public health researchers have criticized as vague (Peltier et al., Lancet Regional Health - Americas, 2026). NIAAA’s definitions of binge drinking (about 5 drinks for men or 4 for women in about two hours) and heavy drinking (5 or more on any day or 15 a week for men; 4 or more or 8 a week for women) still stand.
EPA’s Guide to Air Cleaners in the Home (updated October 1, 2026) gives minimum clean air delivery rates by room size, from 65 cfm for 100 square feet to 390 cfm for 600 square feet: about 0.65 cfm per square foot, close to the common “two-thirds” rule. On an 8-foot ceiling that works out to about 4.9 air changes of filtered air an hour. The chart assumes 8-foot ceilings and a closed room; EPA advises a larger unit for higher ceilings, sizing for the whole space in an open plan, and avoiding devices that make ozone. A purifier also only delivers its rated CADR on its highest setting, which many people turn down because of noise.
EPA’s mold guidance (updated February 18, 2026) says to keep indoor humidity below 60%, ideally 30% to 50%. A single hygrometer reading can mislead: a basement, a closet on an outside wall or the air near a cold window can be far wetter than the middle of the room. Dehumidifiers are rated in pints of water removed per day under test conditions; real removal is lower in a cool basement.
EPA WaterSense says the average American family uses more than 300 gallons a day at home, about 70% indoors, with toilets nearly 30% of indoor use and showers nearly 17%. A family of four with standard fixtures, average leaks and a summer lawn comes out at about 324 gallons a day in our calculator, 71% indoors. The national average hides big differences: the arid West uses far more for landscapes, and the average family loses about 180 gallons a week to leaks, so a single running toilet can change the picture.
Measure instead of assuming. Pour a drink into a measuring cup once; read the gpm on a showerhead and the gpf inside a toilet tank; put a hygrometer in the basement, not the hallway; check the purifier’s CADR for the setting you actually use. Use the rule for its purpose. The standard drink counts alcohol, it does not set a safe amount; the CADR chart sizes a purifier for particles, not for gases or mold; the water average is a benchmark, not a target. Health questions go to a professional. Anyone pregnant, taking medications that interact with alcohol, or finding it hard to cut back should talk to a doctor; SAMHSA’s National Helpline is 1-800-662-4357. Persistent mold or breathing symptoms call for a professional assessment, not a bigger appliance.
NIAAA, What is a standard drink? (updated December 2025) and Drinking levels defined (2023). Peltier et al., Less than what? Response to alcohol consumption recommendations in the 2025-2030 dietary guidelines for Americans, Lancet Regional Health - Americas, 2026, doi:10.1016/j.lana.2026.101510 (PMID 42630529). EPA, Guide to Air Cleaners in the Home (updated October 1, 2026). EPA, A Brief Guide to Mold, Moisture and Your Home (updated February 18, 2026). EPA WaterSense, How we use water, Statistics and facts, Residential toilets and Showerheads (2026). The food storage calculator covers the federal fridge and freezer chart.
A 5 oz pour of 12% wine is 1 standard drink; a 9 oz pour of 14% wine is about 2.1.
EPA’s chart calls for a CADR of about 0.65 cfm per square foot for 8-foot ceilings: 65 cfm for 100 square feet up to 390 cfm for 600; go larger for high ceilings or open plans.
EPA advises below 60%, ideally 30% to 50%, measured with a hygrometer.
EPA says the average family uses more than 300 gallons a day at home, about 70% indoors.
Yes. The 2025-2030 edition, released in January 2026, removed the 2-drink and 1-drink daily limits and advises drinking less for better health.
EPA says air cleaners do not address the cause of mold; fix the moisture source.