Health and nutrition · Sport and hydration
Show a fluid reference: 35 ml/kg and EFSA
Two distinct figures: a 35 ml per kilogram rule of thumb, optionally raised by an internal activity bonus, and the EFSA 2010 adequate intake (2.0 L/day women, 2.5 L/day men, water from drinks and foods). Neither is an order.
Calculate
How the calculator works
The first line multiplies weight by 35 ml, then adds 0 / 250 / 500 / 750 / 1,000 ml by activity rung. Those bonuses are HexaCalc choices, not EFSA opinion values. The second line ignores weight: 2,000 ml if female, 2,500 ml if male, matching EFSA (2010) adequate intakes for total water. The opinion is all sources (beverages + water in food), not a quota of still water glasses. The two results can diverge: that is expected; they are two different constructs. In kidney or heart failure, SIADH, or on some diuretics, “drink more” can be dangerous — the tool does not screen for that. US readers often hear “eight cups”; this engine does not use that slogan.
Formula and method
empirique = 35 × poids(kg) + bonus(activité)
Bonus: 0, 250, 500, 750, or 1,000 ml. Tool rule of thumb, not EFSA.
EFSA = 2 000 ml (femme) ou 2 500 ml (homme)
2010 adequate intake, all water sources, adult population.
EFSA published a 2010 opinion on dietary reference values for water, with adequate intakes of 2.0 L/day (women) and 2.5 L/day (men). An adequate intake is not a measured individual need. The 35 ml/kg rule circulates in popular writing; we implement it as such, without inventing an EFSA pedigree. Heat, altitude, fever, breastfeeding, and long exercise change losses: only our five very coarse bonuses caricature that. Neighboring TDEE does not compute water. US National Academies adequate intakes differ from EFSA; this page still displays EFSA 2.0 / 2.5 L.
Worked example
Woman, 68 kg, light activity
68 kg, female, light rung (+250 ml).
- 35 × 68 = 2,380 ml.
- Plus 250 ml → 2,630 ml (rule of thumb).
- EFSA woman marker: 2,000 ml all sources.
≈ 2,630 ml (weight rule) versus 2,000 ml (EFSA). The gap illustrates two definitions, not a math error.
Man, 85 kg, active
85 kg, male, active rung (+750 ml).
- 35 × 85 = 2,975 ml + 750 = 3,725 ml empirical.
- EFSA man: 2,500 ml all sources.
3,725 ml vs 2,500 ml. The “active” rung pushes the rule of thumb, not the EFSA opinion.
Input notes
- Weight
- Does not enter 2.0 / 2.5 L. A 50 kg adult and a 100 kg adult share the same EFSA figure here.
- Sex
- Switches 2.0 L / 2.5 L. The EFSA opinion is population-level, binary in our implementation as in the cited summary.
- Activity level
- Do not confuse with × 1.55 on calories. Here these are milliliters added to 35 ml/kg only.
Assumptions and limits
Assumptions
- Adult, “average” temperate climate, not a modeled heat wave.
- EFSA = total water (food included), not “tap water only.”
- Activity bonus = tool lump sum.
Limits
- Not a prescription, especially in kidney or heart disease, hyponatremia, medical fluid restriction.
- No sodium, no measured sweat, no outdoor temperature.
- The 35 ml/kg rule is not the EFSA 2010 opinion.
- Children, pregnancy, breastfeeding: outside these two rungs.
How to read the result
If the two numbers diverge, do not “take the larger to be safe” by reflex: in disease, free-water excess exists. In good health, EFSA recalls a population order of magnitude from all sources; thirst, urine, and context (heat, effort) stay more concrete than a milliliter on a screen. Coffee and foods count in total water in the opinion’s sense; we do not invent a caffeine balance.
Common mistakes
Reading 2.5 L as “2.5 L of plain water besides meals.”
EFSA adequate intake includes water in foods and other drinks, not only the carafe.
Adding 35 ml/kg and the 2.5 L EFSA figure.
They are two alternative markers. Adding them has no meaning.
Forcing a large volume while ignoring illness or a drug.
Some situations require restriction. This form does not know that.
Comparison
| Marker | Perimeter |
|---|---|
| 35 ml/kg + bonus | Tool rule of thumb, depends on weight and rung |
| 2.0 L / 2.5 L EFSA 2010 | Population adequate intake, all water sources, independent of weight here |
Related calculations
- TDEE calculatorTDEE here is Mifflin-St Jeor resting metabolism times an activity factor. It includes no deficit, no surplus, and no 1,200 kcal floor.
- Calorie calculatorThree steps: Mifflin-St Jeor resting burn, times a lump activity factor, then a goal offset. The result is an estimate, not a diet.
- Protein calculatorThree coefficients per kilogram: the EFSA PRI 0.83 g/kg for a healthy adult, 1.2 g/kg as an internal “active” rung, 1.6 g/kg as an example in the middle of the 1.4–2.0 g/kg range often cited for training (ISSN 2017).
- Running pacePace is total time divided by distance. Average speed is the inverse. No calories are estimated: ACSM METs are not applied here.
Frequently asked questions
Does 35 ml/kg come from EFSA?
No. EFSA 2010 cites 2.0 and 2.5 L/day (adults, all sources). 35 ml/kg is a separate rule of thumb.
Mixing the two in one source sentence would be incorrect. The page shows them side by side so the difference stays visible.
Does water in food count?
In the EFSA marker, yes: it is total water. In 35 ml/kg, the tool does not specify: it is a volume rule, not a diet balance.
Fruit, vegetables, soups, yogurt contribute. Aiming at 2.0 L only as extra tap water on top of an already watery diet is not what the adequate intake says.
What about sport in high heat?
Our bonuses (up to +1 L) are too coarse for an endurance protocol or a heat wave.
Sweat losses vary enormously. A race hydration plan is built elsewhere. Here, “very active” is only +1,000 ml on the 35 ml/kg rule.
Why link TDEE and calories as related?
Because energy expenditure and hydration cross in real life, not in a shared formula.
Mifflin does not compute water. The link is editorial: after effort or a deficit, “how much to drink” returns. The math stays separate.
Author and update
Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.
- Scientific Opinion on Dietary Reference Values for water (2010) — European Food Safety Authority (EFSA)
Energy expenditure, another estimator
Water does not enter Mifflin. For a caloric order of magnitude, TDEE remains the energy step, with its own lump coefficients.
Open the TDEE calculatorDisplayed volumes are markers (a 35 ml/kg tool rule and EFSA 2010 adequate intake), not a hydration prescription. Some diseases require limiting fluids. Figures on this page are estimates from published formulas, not a diagnosis, not medical advice, and not a personalized eating plan. They do not replace a visit with a clinician. The tool is not designed for children, pregnancy, breastfeeding, eating disorders, or many illnesses and medications. If you are unsure, ask a health professional.
Category: Health and nutrition