How to use it
- Choose your Sex: Male or Female. Both references give separate values for adult men and women. Optionally add your Weight to compare with per-kilogram rules.
- Under Show in, pick liters, US cups or fl oz.
- Read the two adequate intakes, EFSA and US/Canada, in the unit you chose. How this was calculated shows the conversion.
- Use Copy link, Save image or Share to keep the figures.
What "total water" means
Both reference values are for total water. That is all the water a person takes in during a day: plain water, every other drink, and the water inside food.
The National Academies tables put it as water contained in food, beverages and drinking water. EFSA's opinion says the same: drinking water, beverages of all kinds and food moisture.
So the figures are not amounts of plain water to drink. The National Academies estimate that about 20 percent of total water comes from food, and the other 80 percent from drinks.
How the calculation works
The two reference values don't depend on your body: the calculator looks up the adequate intake for the sex you choose and converts it to the unit you pick. Only the optional per-kilogram comparison uses your weight.
The conversions use US customary units: fl oz = liters × 1000 ÷ 29.5735 and US cups = liters × 1000 ÷ 236.588. One US cup is 8 fluid ounces.
| Reference | Sex | Liters | US fl oz | US cups |
|---|---|---|---|---|
| EFSA (2010) | Men | 2.5 | 84.5 | 10.6 |
| EFSA (2010) | Women | 2.0 | 67.6 | 8.5 |
| US/Canada DRI (2004) | Men | 3.7 | 125.1 | 15.6 |
| US/Canada DRI (2004) | Women | 2.7 | 91.3 | 11.4 |
How accurate is this?
These are adequate intakes for groups, not a measured requirement for you. They are total water, so food counts too. Real needs move with heat, activity and body size, which is why EFSA and the US/Canada reference already differ by more than a liter for men.
Why the two references differ
EFSA, the European Food Safety Authority, published its dietary reference values for water in 2010. It set adequate intakes of 2.0 liters a day for women and 2.5 liters for men.
The US/Canada values come from the National Academies report on water, potassium, sodium, chloride and sulfate, released in February 2004. They are 3.7 liters a day for men and 2.7 liters for women.
An adequate intake is used when the evidence isn't strong enough to set an exact requirement. The US/Canada figures are based on average intakes of people who appear to be well hydrated. The two panels worked separately, and the calculator shows both values rather than picking one.
Per-kilogram rules of thumb
Many websites say to drink 30 or 35 ml of water per kilogram of body weight. That rule has no single official source, and neither EFSA nor the National Academies set their adult values per kilogram. For a 70 kg adult, 30 to 35 ml/kg works out to 2.1 to 2.5 liters.
A per-kilogram figure does exist in one official guideline, for a different situation. NICE's guideline on intravenous fluids for adults in hospital (CG174) starts routine maintenance at 25 to 30 ml/kg/day of water. That is a starting prescription for a drip, adjusted by clinicians, not a drinking target. The calculator shows it only so you can see where the per-kg numbers people quote sit.
Add your Weight and the result shows all three per-kg figures next to the adequate intakes.
What the numbers tell you, and what they don't
EFSA notes that its values apply to moderate temperatures and moderate physical activity. The National Academies note that very active people and people in hot climates may need more water.
The same National Academies release says healthy people generally meet their needs by letting thirst guide them. It also says the panel gives no rule of thumb about glasses of water per day.
The figures are averages for healthy adults, not a measurement of one person. They are not made for pregnancy, breastfeeding, kidney or heart conditions, or children. Those cases have their own values or need a professional.
Related calculators
Water is often looked at alongside other daily references. The protein calculator turns the published protein figures into grams for your weight. The sleep calculator works out bedtimes from 90-minute cycles.
Questions
- Does the amount include coffee, tea and food?
- Yes. Both references count total water: plain water, all other drinks and the water in food. The National Academies estimate that food supplies about 20 percent of it.
- How many cups of water is 2.7 liters?
- About 11.4 US cups, or 91.3 fl oz. Pick US cups or fl oz under Show in to see any of the four values that way.
- Does my weight change the result?
- Not the main figures. Neither EFSA nor the National Academies set their adult values per kilogram of body weight; they give one figure for men and one for women. If you add your weight, the calculator also shows the 30 and 35 ml/kg rules of thumb and NICE's 25–30 ml/kg hospital maintenance figure, clearly labeled, for comparison.
- Is "8 glasses a day" an official figure?
- Not in these sources. The National Academies release states that it offers no rule of thumb based on how many glasses of water to drink each day.
- Which value applies to me, EFSA or US/Canada?
- Both are official reference values for healthy adults, set by different bodies from different data. The page shows both so you can compare them.
- Do the values change in hot weather or with exercise?
- EFSA's figures assume moderate temperatures and activity. The National Academies note that very active people in hot weather often have total water needs of 6 liters or more.
- How much do I sweat during exercise?
- It varies a lot between people. The sweat rate calculator works it out from your weight before and after a session.