Hydration Calculator
Estimate how much water you need each day based on your weight and activity.
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Hydration Calculator
Runs in your browser — we never see your numbers.
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General guide only — not a diagnosis or medical advice.
How much water is enough?
A simple rule of thumb is about 30–35 ml of fluid per kg of body weight each day, plus roughly 350 ml for every 30 minutes of exercise and a little more in hot weather.
Signs you need more
- Dark yellow urine or going to the toilet rarely
- Headache, tiredness or dizziness
- Dry mouth and lips
People with kidney or heart conditions may be advised to limit fluids — follow your doctor’s advice.