Water Intake Calculator
How much water you actually need each day.
The '8 glasses a day' rule ignores your size and your activity. This calculator scales your water needs to your body weight and adds extra for exercise. It's a baseline for plain water — food, coffee and climate all nudge the real number.
How it's calculated
Baseline ≈ 35 ml per kg of body weight, plus ≈ 360 ml per 30 minutes of exercise; a glass is counted as 250 ml.
Frequently asked questions
Is 8 glasses a day actually right?
It's a decent average that happens to suit a ~70 kg adult — but a 50 kg office worker and a 100 kg athlete have very different needs. Scaling to body weight, as this calculator does, is more honest.
Does coffee count toward hydration?
Mostly yes — coffee's mild diuretic effect doesn't cancel out its water content for regular drinkers. But water remains the simplest baseline to track.
Can you drink too much water?
Yes, though it's rare: overhydration (hyponatremia) mostly affects endurance athletes drinking far beyond thirst. For daily life, pale-yellow urine is a better guide than any number.