Water Intake Calculator
Estimate how much water you should drink per day based on body weight, exercise time and climate — in litres, ml, cups and bottles.
How the estimate works
Daily fluid ≈ 35 ml × weight (kg) + 350 ml per 30 min exercise + 500 ml in hot climates
The 35 ml/kg baseline covers normal living in a temperate climate. Exercise adds sweat loss; heat and humidity add
more. Remember that around a fifth of intake usually arrives via food — soups, fruit and vegetables all count.
Worked example
70 kg, 30 minutes of exercise, temperate climate:
70 × 35 ml = 2.45 L, plus 0.35 L for exercise = about 2.8 litres —
call it 11 glasses spread across the day.
Signs you're getting it right
- Urine is pale yellow; dark yellow suggests you're behind.
- You rarely feel thirsty during normal activity.
- For long workouts, body weight is stable before vs. after (each kg lost ≈ 1 L of sweat to replace).
Frequently asked questions
How much water should I drink a day?
A common evidence-informed baseline is about 35 ml per kilogram of body weight — roughly 2.5 litres for a 70 kg adult — plus extra for exercise and hot weather. Thirst and pale-yellow urine are the practical day-to-day guides.
Does tea, coffee or food count?
Yes. Roughly 20% of fluid intake typically comes from food, and caffeinated drinks still hydrate on balance. The target here is total fluid, not plain water only.
How much extra should I drink when exercising?
A practical rule is about 350 ml for every 30 minutes of moderate exercise — more in heat or if you sweat heavily. Weighing yourself before and after long sessions shows your actual sweat loss (1 kg ≈ 1 litre).
Can I drink too much water?
Yes — drinking many litres in a short period can dangerously dilute blood sodium (hyponatremia). Spread intake through the day, and if you have kidney or heart conditions, follow your doctor’s fluid guidance rather than a calculator.
This tool provides general health information, not medical advice. If you have kidney, heart or other conditions affecting fluid balance, follow your doctor's guidance.