Water Intake Calculator
Estimate how much water to drink each day based on your weight and activity.
How to use
- Enter your weight.
- Add your typical daily exercise.
- See your suggested daily water intake.
How the Water Intake Calculator works
Estimates a daily fluid target from bodyweight, with an added allowance for exercise.
It uses roughly 35 ml per kilogram of bodyweight as a baseline, then adds about 350 ml for every 30 minutes of exercise to cover sweat losses.
ml/day = weight(kg) × 35 + (exercise minutes ÷ 30) × 350
Worked example
A 70 kg person doing 60 minutes of exercise: 2,450 + 700 = about 3.2 litres a day.
Things worth knowing
- This counts total fluid, not just plain water. Tea, coffee, milk and the water in food all contribute — food typically supplies about 20% of intake.
- Hot climates, altitude, illness, pregnancy and breastfeeding all raise requirements.
- Thirst and urine colour are decent everyday guides. Pale straw is about right; consistently dark suggests you need more.
Frequently asked questions
Is more always better?
No — needs vary with climate, health and diet. This is a general guide, not a strict target.
Do other drinks count?
Most fluids and water-rich foods contribute to hydration, but plain water is the best baseline.
Is the 8 glasses a day rule real?
It has no strong scientific basis. Requirements scale with body size, activity and climate, which is why this calculator uses weight rather than a fixed count.
Does coffee dehydrate you?
Not at normal intakes. The diuretic effect is mild and outweighed by the fluid in the drink itself.