How much water do you need?
Daily water needs vary with body size, activity, climate and diet. A common rule of thumb is about 30-35 ml of fluid per kilogram of body weight, with extra added for exercise. This calculator uses that base and adds roughly 350 ml for each 30 minutes of activity to give a practical daily target.
Reading the result
The figure is total fluid, not only plain water — food and other drinks contribute too, especially water-rich fruit and vegetables. Use the glasses estimate as an easy way to spread intake across the day rather than drinking it all at once. Thirst, and the colour of your urine (pale straw is a good sign), are useful real-world checks.
Tips to stay hydrated
- Keep a bottle within reach and sip through the day.
- Drink more in hot weather or when exercising.
- Water-rich foods count toward your total.
- Very dark urine usually means you need more fluid.
Frequently asked questions
Does coffee count?
Yes, in moderation it still contributes fluid, though water is the best everyday choice.
Is this exact?
No — it's a practical estimate. Adjust to thirst, climate and how you feel.
Is my data private?
Yes — everything is calculated in your browser.