How much water you actually need
A sensible daily target — scaled to you, not a flat “8 glasses”.
Results update as you type 🥑
How much water, really
The “8 glasses” rule has no strong evidence. A better starting point is roughly 30–35 ml per kg of bodyweight, adjusted up for exercise, heat and altitude.
About 20% of your water comes from food, and other fluids count. This calculator gives a total target — you do not need to drink all of it as plain water.
Thirst is a reliable guide for most healthy people. Pale-yellow urine means you are well hydrated; dark means drink more.
Common questions
Does coffee or tea count?
Yes. The mild diuretic effect of normal caffeine intake does not cause net dehydration; these fluids still hydrate you.
Can I drink too much water?
Rarely, but yes — excessive intake in a short time can dilute sodium (hyponatremia). Spread intake across the day.
Do I need electrolytes?
For long or very sweaty sessions, yes. For everyday hydration, a normal diet covers it.
Is my data stored?
No. Everything is calculated in your browser. Nothing is sent to a server or saved.
Sources & references
- Mifflin MD, St Jeor ST, et al. “A new predictive equation for resting energy expenditure in healthy individuals.” Am J Clin Nutr. 1990;51(2):241–247.
- Frankenfield D, Roth-Yousey L, Compher C. “Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults.” J Am Diet Assoc. 2005;105(5):775–789.
This calculator provides estimates for general educational use and is not medical advice. Consult a qualified professional before making significant dietary changes.