Water Intake Calculator
Estimate how much water to drink each day.
How to use
- 1 Enter your body weight.
- 2 Pick the unit, kilograms or pounds.
- 3 Choose your activity level for the day.
- 4 Tick "Hot climate" if it is warm where you are.
- 5 Read your target in litres, millilitres, ounces and glasses.
About Water Intake Calculator
The Water Intake Calculator estimates how much water you should aim to drink in a day based on your body weight and how active you are.
Enter your weight in kilograms or pounds, choose an activity level, and tick the hot-climate option if the weather is warm.
The tool returns your recommended intake in four convenient units at once: litres, millilitres, US fluid ounces and an approximate number of 250 ml glasses, so you can track it whichever way suits you.
The estimate starts from a widely used rule of thumb of about 35 millilitres of water per kilogram of body weight, then adds an allowance for moderate or vigorous activity and a little extra for hot conditions, where you lose more fluid through sweat.
Staying adequately hydrated supports energy, concentration, temperature regulation and digestion, and a concrete daily target makes it far easier to build the habit.
Everything runs locally in your browser — your weight and choices are never uploaded or stored.
Remember that this is a general guide, not medical advice: actual needs vary with health conditions, pregnancy, medication and the food you eat, much of which also contains water.
If you have a medical condition affecting fluid balance, follow your clinician’s guidance.
FAQ
How is the recommendation calculated?
It uses about 35 ml of water per kilogram of body weight as a baseline, then adds a fixed amount for moderate or active days and a little more for a hot climate.
Does food and other drinks count?
Yes. Much of your daily fluid comes from food, tea, coffee and other drinks, so you rarely need to hit the full figure from plain water alone.
Is this medical advice?
No. It is a general estimate. Needs change with health conditions, pregnancy and medication, so consult a clinician if you have specific concerns about fluid intake.