Guide
How Much Water You Should Drink (and How It Is Estimated)
Learn how daily water intake is estimated from weight and activity, and the factors that change your needs.
A water intake calculator estimates a daily hydration goal from your body weight and activity level. It gives a personalised target where the generic "eight glasses a day" is too blunt.
How water intake is estimated
A common rule of thumb is about 30–35 ml of water per kilogram of body weight per day, increased for activity and hot climates. The calculator applies this baseline and adds extra for exercise to produce a daily target in litres and ounces.
Factors that change your needs
- Exercise — add water to replace sweat loss.
- Hot or humid climates — higher baseline.
- Pregnancy and breastfeeding — increased needs.
- Illness, fever, or altitude — drink more.
How to use the calculator
- Enter your weight.
- Choose your activity level.
- Read your estimated daily water goal in litres and ounces.
Examples
A 70 kg person with a baseline of 35 ml/kg needs about 2.45 litres (roughly 83 oz) per day. With moderate exercise, the target might rise to about 3 litres. A 90 kg person starts closer to 3.15 litres before activity.
When a water intake calculator is useful
- Setting a daily hydration goal that fits your body size.
- Adjusting water intake for exercise or hot weather.
- Building a healthy drinking habit with a concrete target.
- Comparing your usual intake against an estimated need.
Put it into practice
Use the Water Intake Calculator right now — free, in your browser, no sign-up required.
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