About the Water Intake Calculator
This gives a rough guide to how much water to aim for in a day, based on your body weight and how much you exercise. Staying hydrated supports energy, concentration and general health, and a personalised target based on your size is more useful than the generic "eight glasses." Enter your weight and daily exercise to see a suggestion in litres, fluid ounces and glasses.
How it works
It uses a common rule-of-thumb: about 35 ml of water per kilogram of body weight per day, plus roughly 350 ml for every 30 minutes of exercise to replace what you lose through sweat. The total is shown in litres, US fluid ounces, and 250 ml glasses. For example, a 70 kg person doing 30 minutes of exercise gets about 2.45 L + 0.35 L ≈ 2.8 L a day.
Assumptions and behaviour
- Based on ~35 ml per kg plus an exercise top-up — a widely-cited general guideline.
- The figure is total water, and a good portion comes from food and other drinks, not just plain water.
- Glasses are counted as 250 ml each.
- Imperial weight is converted to kilograms for the calculation.
Limitations
- This is a general estimate, not a prescription. Real needs vary with climate, humidity, altitude, illness, pregnancy or breastfeeding, and individual physiology — you'll need more in heat or when unwell.
- You can drink too much water. Excessive intake in a short time can dangerously dilute blood sodium (hyponatraemia); this tool suggests a daily total, not a rate.
- Some conditions (kidney or heart problems) require a doctor-set fluid limit — follow medical advice over any calculator.
- Thirst and urine colour are practical everyday guides alongside a target.
- This is general information, not medical advice.
Privacy
The calculation runs entirely in your browser. Your details are never uploaded or stored.
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