Water Intake Calculator
Hydration needs scale with body size, so the two-litre-a-day rule fits some people and starves others. This calculator applies a weight-based guideline used by sports dietitians, letting you choose an activity level that matches your week. You get a target in litres and the same figure in 250 ml glasses, which is easier to act on than an abstract number when you are deciding whether to fill the bottle again.
Enter values
Results
- Daily water target
- 2.45 L
- In millilitres
- 2,450 ml
- 250 ml glasses
- 9.8
- Rule applied
- 35 ml per kg of body weight
How is the Water Intake calculated?
Pick your weight and the option that best describes your routine. The calculator multiplies your weight by a millilitres-per-kilogram factor: thirty for mostly sedentary days, thirty-five for a typical day and forty for training, heat or long hours on your feet. It converts the result into litres, then divides by zero point two five for glasses of two hundred and fifty millilitres. Food and other drinks count towards the total, so treat the output as total fluid rather than plain water.
Formula
Daily fluid (ml) = weight in kg × factor, where factor = 30 ml/kg mostly resting, 35 ml/kg typical, 40 ml/kg active or hot. Litres = ml ÷ 1000. Glasses = ml ÷ 250.
Example
A 70 kg person choosing a typical day gets 70 × 35 = 2450 ml, which rounds to 2.45 litres, or 2450 ÷ 250 ≈ 9.8 glasses of 250 ml. The same person on a training week picks forty millilitres per kilo and lands at 2800 ml, about 2.8 litres and eleven glasses, while a desk-bound week at thirty millilitres per kilo gives 2100 ml, roughly eight glasses. Spreading those glasses across waking hours keeps the target reachable.
Things to remember
Pale straw urine usually means you are close, while a consistently dark colour suggests topping up, and hot weather or hard sessions deserve extra on top. Build the habit around fixed moments, such as with each meal and after training, and the daily total tends to look after itself.
Frequently Asked Questions
How much water should I drink per day?
This calculator estimates thirty to forty millilitres per kilogram of body weight depending on activity, which lands most adults between two and three litres of total fluid. Sweat, heat and altitude push the number up, while a quiet day at a desk sits at the lower end.
Does coffee and tea count towards my intake?
Yes, the mild diuretic effect of caffeine is far outweighed by the fluid it delivers, so coffee, tea and milk all count towards the daily total. Alcoholic drinks hydrate far less effectively and come with their own fluid swings, so it is worth having water alongside them.
Can I drink too much water in a day?
Yes, and it is rare but serious: extremely large intakes can dilute blood sodium in a condition called hyponatraemia. For healthy people following a weight-based target, the practical safeguard is to drink to thirst on top of a sensible baseline rather than forcing litres past comfort.
Should my water intake change when I exercise?
It should, because an hour of sweating can remove hundreds of millilitres of fluid. Drink before, during and after sessions, and add roughly half a litre for every kilo lost during training.
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