How to use the water intake calculator
- Enter your weight (switch between kg and lb).
- Add your daily exercise minutes and pick your climate.
- See your estimated daily target in litres, cups and glasses.
How much water do you actually need?
A common starting point is around 30–35 ml of water per kg of body weight per day, with extra for exercise (roughly 350–500 ml per 30 minutes) and for hot or humid conditions. But total fluid needs include what you get from tea, coffee, milk and food — fruit and vegetables contribute a surprising amount. The old "8 glasses a day" rule isn't based on strong evidence; the better guide is to drink when thirsty and check that your urine is pale straw-coloured rather than dark.
Benefits
- Estimates a daily water target from weight, exercise and climate.
- Shows the result in litres, cups and fluid ounces.
- Metric and imperial input.
- Private — calculated in your browser.
Limitations to know
- It is a general estimate, not a medical prescription.
- It does not account for pregnancy, illness or medications that change fluid needs.
- Some heart and kidney conditions require restricting fluids.
Common mistakes to avoid
- Ignoring that tea, coffee, milk and food all contribute to daily fluid intake.
- Drinking a very large volume quickly instead of spreading it through the day.
- Chasing a number instead of listening to thirst and checking urine colour.
Alternatives
For calorie needs use the BMR & TDEE Calculator; for weight category use the BMI Calculator.
Last updated: August 2026 · Reviewed by the AI Toolbox editorial team.
Frequently asked questions
Do tea and coffee count?
Yes — despite the myth, moderate caffeinated drinks still contribute to your daily fluid intake.
Can you drink too much water?
Yes. Drinking excessive amounts very quickly can dangerously dilute blood sodium (hyponatraemia). Spread intake through the day.
Is this medical advice?
No — it's a general estimate. Some heart and kidney conditions require fluid restriction, so follow your doctor.
Is my data stored?
No — it's calculated in your browser.