Daily Water Intake Calculator
How much water you need scales with how much body you have and how much you sweat. This calculator gives a practical daily baseline from bodyweight and activity level, in liters and fluid ounces. Treat it as a starting point — thirst, urine color, and climate matter more than hitting a number exactly.
Fill in the fields above to see your result.
How it's calculated
The baseline is about 35 ml of water per kilogram of bodyweight per day — a widely used clinical rule of thumb that lands close to the adequate-intake values published by the European Food Safety Authority and the U.S. National Academies once food moisture is accounted for. An 80 kg person gets a 2.8 L baseline. This per-kilogram approach beats one-size-fits-all rules like '8 glasses a day' because fluid needs are driven primarily by body mass.
On top of the baseline, the calculator adds an activity bump that grows with your training load — from nothing when sedentary up to about 1.5 L per day for very active people. Exercise raises fluid needs mainly through sweat, and typical sweat rates run 0.5-2 L per hour depending on intensity, climate, and the individual. The bump is deliberately a middle-of-the-road allowance: a hard session in the heat can exceed it, an easy lifting session in air conditioning won't reach it.
Two honest caveats. First, all fluids and food count toward hydration — coffee, tea, and the water in fruit and vegetables all contribute; the target is total fluid, not plain water only. Second, the best day-to-day gauges are cheap and built in: pale-yellow urine and rarely feeling thirsty mean you are hydrated regardless of what any calculator says. Use the number as a floor to check yourself against on training days, when athletes most commonly under-drink, rather than a ceiling to force on rest days.
Frequently asked questions
How much water should I drink a day?
About 35 ml per kg of bodyweight, plus extra on training days — roughly 2.8 L for an 80 kg person. Thirst and pale-yellow urine are the best real-time checks.
Do coffee and tea count toward my water intake?
Yes. The mild diuretic effect of caffeine doesn't offset the fluid delivered. Total fluid from all drinks and food is what your body actually uses.
How much extra should I drink on training days?
Typical sweat rates are 0.5-2 L per hour of exercise. Weigh yourself before and after a session — each kilogram lost is roughly a liter to replace.
Can you drink too much water?
Yes — extreme intakes over short periods can dangerously dilute blood sodium (hyponatremia). Spread intake through the day and don't force large volumes rapidly.
Take it with you
Every calculator, plus workout and macro tracking, in the ElevenSix Fitness app for iPhone.