Water Intake Calculator
Roughly 30–35 ml per kg of body weight from all sources, plus replacement for what you sweat out. The eight-glasses rule has no scientific origin.
Your results
Includes fluid from food, tea and coffee — not just water you drink deliberately. Urine colour is a more useful day-to-day check than any target.
What the numbers mean
The baseline is around 33 ml per kg of body weight per day from all sources. Food typically supplies 20–30% of it, and tea and coffee count — caffeine's mild diuretic effect is more than offset by the fluid in the drink.
Training adds roughly 500–750 ml per hour, more in heat. Sweat rates vary enormously between people, which is why a single number cannot be precise.
Why over-drinking is not better
Excess water is simply excreted; there is no reserve to build. Constantly clear urine is a signal to drink less, not a sign of doing well. In extreme cases — usually endurance events where large volumes of plain water are consumed while sodium is lost in sweat — dilution of blood sodium is genuinely dangerous.
Pale straw urine is the practical check. Dark yellow means drink more.
Common questions
Does coffee count?
Yes. Coffee and tea contribute to your fluid intake.
How do I know if I am dehydrated?
Urine colour is the practical check. Being 2% dehydrated costs roughly 2% of strength and around 10% of high-intensity endurance.
Do I need electrolytes?
Only for long or hot sessions. Sodium is the only electrolyte lost in meaningful quantities in sweat.
Should I drink to a schedule?
Drinking to thirst plus a little extra around training is sufficient for almost everyone.
Related calculators
Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
