Water Intake Calculator
Estimate how much water to drink each day based on your weight, activity level and climate. You'll get the target in litres, millilitres, cups and fluid ounces. Updates as you type.
A general-guidance estimate using common formulas — not medical advice. If a health condition affects your fluid intake, follow your doctor.
How it works
daily fluid ≈ 35 ml × kg + activity allowance + climate allowance
- Base: about 35 ml per kg of body weight (≈ 2.5 L for a 70 kg adult).
- Activity: adds roughly 350 ml per half-hour band of daily exercise.
- Climate: warm/hot conditions add 300–600 ml for extra sweat loss.
- This is total fluid — about 20% typically comes from food and other drinks, so plain water can be a little less.
FAQ
How much water should I drink a day?
A common starting point is about 30–35 ml per kilogram of body weight — roughly 2–3 litres a day for most adults. The old "8 glasses" rule is a fair average, but real need rises with weight, exercise, heat and illness. This calculator scales to your weight, activity and climate.
Does food and other drinks count toward water intake?
Yes. About 20% of intake comes from food, and drinks like milk, tea and coffee count too (coffee's diuretic effect is mild). So your drinking-water target can be a little lower than your total fluid need; this tool estimates total fluid.
How does exercise change how much water I need?
Exercise raises water loss through sweat — often an extra 350–700 ml per hour, more in heat. The calculator adds an allowance for your activity level. For long sessions, drink before, during and after, and consider electrolytes for sweaty workouts over an hour.
Can you drink too much water?
Yes, though it's uncommon. Very large amounts in a short time can dilute blood sodium (hyponatremia). Aim for steady hydration through the day. Pale-yellow urine is a simple sign you're well hydrated; dark urine means drink more.
Is this calculator medical advice?
No — it's a general-guidance estimate. Needs vary with health conditions, medications, pregnancy and climate. If you have a heart, kidney or other condition affecting fluid intake, follow your doctor's guidance.
More health tools: BMI calculator, calorie calculator, and the full tools list.