Water Intake Calculator
“Eight glasses a day” ignores that a 120-lb office worker and a 220-lb athlete have very different needs. This calculator sets your hydration target from body weight and activity — food water included in the thinking.
Includes water from food (~20% of intake). Pale-yellow urine is the real-world check — adjust up if it’s dark.
The guideline
Sedentary adults land near 30 ml/kg; active people and hot climates push toward 40 ml/kg. About 20% of that typically comes from food — fruit, vegetables, soups — so your drinking target is a bit lower than the total.
Signs you’re on track
- Pale-straw urine color through the day.
- Steady energy without the 3 p.m. fog (mild dehydration is a common culprit).
- You’re not forcing gallons — overhydration is real, especially around endurance events.
Frequently asked questions
How much water should I drink daily?
Roughly 30–40 ml per kg of body weight, adjusted for activity and heat. For most adults that’s 2–3.5 liters of total water.
Does coffee dehydrate you?
Not meaningfully — coffee’s mild diuretic effect is offset by its water content. It counts toward hydration.
Can you drink too much water?
Yes (hyponatremia), though it’s rare outside endurance events. Don’t force far beyond thirst without reason.
Do I need electrolytes?
For sessions over ~90 minutes or heavy sweating, yes. For normal days, food covers it.
Is the 8-glasses rule wrong?
It’s a fine average that happens to undershoot big active people and overshoot small sedentary ones — which is why weight-based targets win.