Water intake calculator
Estimate daily drinking water from body weight: 35 ml/kg as the clinical baseline, ACSM 2007 exercise replacement of 400–800 ml per hour (500 ml used here), a 10–20% uplift in hot weather, and +300 / +700 ml for pregnancy and breastfeeding from the IOM 2004 water intake report — reported in litres and cups.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Weight and routine
This covers drinking water only, not the water in food. Anyone on a fluid restriction for kidney or heart disease should follow medical advice.
Result
Enter your weight, then press “Calculate water”.
What this tool does
- Before a summer run or ride, work out how much extra to drink for the session instead of relying on thirst alone.
- For desk workers, sanity-check the baseline: 70 kg lands at about 2.45 L, which fits body weight far better than the “eight glasses” rule.
- Estimate the extra allowance during pregnancy or breastfeeding (+300 ml / +700 ml) and size your bottle and reminders around it.
- Plan long hikes or work in the heat with the climate uplift (+10% / +20%) to cut the risk of heat exhaustion.
Example
Input
Weight 70 kg, 0 minutes of exercise, temperate, no special status
Output
Baseline 2450 ml, recommended 2450 ml per day (2.45 L, about 10.2 × 240 ml cups)
Switch to 60 minutes of exercise in hot weather and the result becomes (2450 + 500) × 1.1 = 3250 ml.
Frequently asked questions
Is “eight glasses a day” right?
Eight glasses is about 2 L, which is roughly right for a 60–70 kg adult but ignores weight, training load and temperature. The 35 ml/kg rule this tool uses scales with body weight: 50 kg needs 1.75 L while 90 kg needs 3.15 L — a big spread.
How much should I drink while training?
The ACSM 2007 position stand recommends 0.4–0.8 L per hour of exercise, depending on your sweat rate; this tool uses the 500 ml/hour midpoint. For precision, weigh yourself before and after: each kilogram lost calls for about 1.25–1.5 L of replacement.
Can drinking too much water be dangerous?
Yes, but it takes a large volume in a short window — usually several litres — faster than the kidneys can excrete, leading to hyponatraemia. Spreading the amount from this tool across the day is safe; for marathons and ultra events, include sodium in your drink.
Does this include water from food?
No. The IOM 2004 figures of 3.7 L for men and 2.7 L for women are total water, roughly 20% of which comes from food. This tool estimates what you actually need to drink, so the number sits below that total.
Do coffee and tea count?
They do. Coffee and tea at normal intakes do not cause net dehydration and can be counted towards fluid intake, though sugary drinks and alcohol are not good hydration choices.
Keywords：water intakedaily waterhydration calculatorhow much wateracsm fluid replacement每日饮水量喝水计算饮水量补水量运动补水一天喝多少水hydration