Get a rough daily water target from your body weight, with extra added for exercise. The result is shown in litres and as 250 ml glasses so it’s easy to act on. This is a general guideline — not a medical prescription — and it runs entirely on your device.
Enter your weight to estimate daily water.
A general guideline based on body weight and activity, counting all fluids — not medical advice. Needs rise with heat, illness and pregnancy. People with kidney, heart or liver conditions should follow their doctor’s guidance.
How it works
The baseline uses about 33 ml of water per kilogram of body weight, a common rule of thumb: a 70 kg person gets roughly 2.3 litres. Exercise adds around 350 ml for every 30 minutes of activity to replace what you sweat out, so an hour of training adds about 700 ml.
This total counts all fluids, and food contributes too — fruit, vegetables and soups can cover a fifth of your intake. Treat the number as a target for the day’s drinks, not water you must sip on top of everything else, and adjust up in heat, at altitude, or when unwell.
Practical examples
A typical day
At 70 kg with no exercise, the estimate is about 2.3 litres — roughly nine 250 ml glasses spread across the day.
After a workout
The same person who trains for an hour adds about 700 ml, bringing the target to around 3 litres to cover sweat losses.
A hot Belgrade summer
On a 35°C day, add noticeably more than the estimate: heat and sweating raise needs beyond what weight and exercise alone predict. Thirst and pale-yellow urine are better real-time guides.
Frequently asked questions
Is “8 glasses a day” actually correct?
It’s a rough rule that happens to land near many people’s needs, but it isn’t based on body size or activity. This calculator scales with your weight and exercise, which is more individual — though still just an estimate.
Does coffee, tea or juice count?
Yes. All fluids contribute to hydration, including coffee and tea — their mild diuretic effect doesn’t cancel out the water they contain. Water is best for most of your intake, but the target covers total fluids.
Does food count toward the total?
Partly. Water-rich foods like fruit, vegetables, yoghurt and soup can supply roughly 20% of daily fluid. That’s one reason you don’t need to drink the entire figure as plain water.
How does exercise change the amount?
The tool adds about 350 ml per 30 minutes of activity to replace sweat. Intense sessions, heat and heavy sweating can need more, plus electrolytes for long or very intense efforts — this is a general allowance, not a sports-hydration plan.
Can you drink too much water?
Yes, though it’s uncommon. Drinking far more than needed in a short time can dilute blood sodium (hyponatraemia), which is dangerous. Spread intake through the day and don’t force large volumes well beyond thirst.
How do I know if I’m hydrated?
Pale straw-coloured urine and infrequent thirst are good everyday signs. Dark urine suggests you need more. These real-time cues beat any formula, which is why the estimate is a starting point rather than a strict quota.
Should some people not follow this estimate?
Yes. People with heart, kidney or liver conditions, or on fluid restrictions, should follow their doctor’s guidance instead. Needs also change in pregnancy and breastfeeding. When in doubt, ask a professional.
Are my inputs kept private?
Yes. The calculation runs entirely in your browser; nothing is uploaded and analytics never receives your weight or activity.
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