Water intake calculator
Estimate how much water your body needs per day.
Approximate daily water needs
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Add 500-1000 ml on hot days or when training.
A popular rule of thumb is 30-35 ml per kilogram of body weight per day - for most adults that is 1.5-2.5 litres. Water from food and other drinks counts too.
Fatigue and headaches often signal dehydration before thirst does - which is why logging your intake through the day is the easiest way to stay on top of it.
This calculator is approximate and educational - it does not replace advice from a doctor or dietitian.
Frequently asked questions
Do coffee and tea count toward hydration?
Yes, they usually count as fluids. Plain water is still the simplest base, especially in hot weather, after training or when appetite is lower.
Do I need to drink exactly what the calculator shows?
No. The result is approximate. Needs rise with heat, activity, fever and higher body weight, and some water also comes from food.
How can I tell I am drinking too little?
Common signs include thirst, darker urine, headache, tiredness and dry mouth. If symptoms are strong or unusual, contact a doctor.
Can I drink too much water?
Yes, although it is uncommon in healthy people. Very large amounts in a short time can be dangerous, especially without electrolytes.
Does water from food count?
Yes. Fruit, vegetables, soups and yogurt all provide fluid. That is why the calculator gives guidance, not a strict rule.
How much should I drink during exercise?
Often add 500-1000 ml depending on sweat, duration and temperature. Electrolytes matter during longer efforts.
Is urine color a good hydration marker?
It is a simple clue, not a perfect test. Dark urine can suggest low fluids, while supplements and medicines can change color too.
Is it easier to underdrink on GLP-1?
For some people, yes. Lower appetite can also mean less drinking and less water from food, so reminders and logging help.
Do zero-calorie drinks count?
Usually yes. If they replace plain water entirely or increase sweet cravings, watch your own response.
Does alcohol hydrate?
Do not treat alcohol as hydration. It can increase fluid loss and make calories and sleep harder to manage.
Should I drink a lot at once?
No. Spreading fluids through the day is easier. Large amounts at once are uncomfortable and often just send you to the bathroom.
When should I ask a doctor about fluids?
With kidney or heart disease, swelling, pregnancy, diuretics or fluid restrictions, do not set your target alone.