Water Intake Calculator
Your size, training and the weather set your real need. Here it is in litres — and in 500 ml bottles, which is how people actually drink.
Where the target comes from
The base is roughly 33 ml per kilogram of body weight — the middle of what health authorities recommend for adults. Training adds about 350 ml per half hour to replace sweat, and hot climates add up to 800 ml on top. A 75 kg person training 30 minutes in mild weather lands near 2.8 litres.
“Eight glasses a day” is not wrong so much as unscaled — right for a small sedentary adult, far short for a big man training in summer.
Signals that beat any calculator
- Urine colour is the honest gauge: pale straw is right, apple-juice dark means drink, fully clear means you can ease off.
- Thirst works for everyday life — it just lags during hard training and in older adults, which is where a target helps.
- Weigh-in after long sessions: every kilogram lost is a litre of sweat to put back.
Hydration and “water weight” work backwards from what most people expect. Drinking consistently signals the body to retain less, not more. The bloated look tracks sodium spikes and irregular drinking far more than total volume.
Does it help with fat loss?
Indirectly but usefully: water before meals modestly reduces how much people eat, thirst is routinely misread as hunger, and swapping one 140-kcal soda for water is 980 kcal a week gone without willpower. Pair the target here with your numbers from the calorie calculator.
Frequently asked questions
Do coffee and tea count?
Yes. The diuretic effect of normal caffeine intake is far too small to cancel the fluid. Alcohol is the exception that genuinely dehydrates.
Can I drink too much?
It takes real effort, but yes — litres in a short window can dilute blood sodium dangerously. Spread intake across the day and add electrolytes around very long sweaty sessions.
Why am I thirsty at night?
Usually a salty dinner or a dry bedroom. Front-load your drinking earlier in the day so the fix is not a 3 a.m. bathroom trip.