How much water you should drink
Staying properly hydrated supports everything from concentration and energy to digestion and temperature regulation. The old "eight glasses a day" rule is a rough average that ignores body size, activity, and climate — all of which change how much fluid you actually need. This calculator gives a more personalised estimate.
How to use the calculator
Enter your body weight, choose your activity level, and select your climate. The result is shown in litres, and also translated into cups and standard bottles so it is easy to picture across a day.
How the estimate is built
The baseline is roughly 35 mL of water per kilogram of body weight, so a 70 kg person needs about 2.45 litres in a temperate climate at rest. Activity and heat act as multipliers, because exercise and sweating increase fluid loss significantly — hard training or a hot, dry climate can push your needs 20% or more above the baseline.
Practical hydration tips
You do not have to drink all of this as plain water: around 20% of most people's fluid comes from food, especially fruit and vegetables, and tea and coffee count too despite being mild diuretics. A simple self-check is urine colour — pale straw suggests good hydration, while dark yellow is a sign to drink more. Sip steadily through the day rather than gulping large amounts at once, and drink extra around exercise.