Water intake calculator: litres a day by body weight
Find out in seconds how many litres of water to drink a day. We estimate it from your body weight, activity level and climate, using the clinical reference of about 35 ml per kg, with adjustments for training and heat.
Climate
Rough estimate (drinking water; food adds more on top). Not medical advice.
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How is your water need calculated?
We start from a base of about 35 ml of water per kilo of body weight — the most widely used reference for healthy adults — and adjust it. Training adds roughly 500-750 ml per hour of exercise, because that is the order of magnitude most people sweat. Heat adds more. The result is a target for total fluid, not for glasses of plain water: coffee, tea, milk, soup and the water in fruit and vegetables all count towards it, and food alone typically supplies 20-30% of the total. Treat the number as a starting reference and let thirst and urine colour do the fine-tuning — they are better instruments than any formula.
How much water to drink a day by body weight
Litres a day for each body weight, depending on how much you move and whether it is hot. The two-litres-for-everyone rule makes little sense: at the same activity, a 90 kg person needs almost twice as much as a 50 kg one.
| Weight | Sedentary | Exercise 3-5 days | Active and hot |
|---|---|---|---|
| 50 kg | 1.8 L · 7 glasses | 2.0 L · 8 glasses | 2.3 L · 9 glasses |
| 60 kg | 2.1 L · 8 glasses | 2.4 L · 9 glasses | 2.8 L · 11 glasses |
| 70 kg | 2.5 L · 10 glasses | 2.8 L · 11 glasses | 3.3 L · 13 glasses |
| 80 kg | 2.8 L · 11 glasses | 3.2 L · 13 glasses | 3.7 L · 15 glasses |
| 90 kg | 3.2 L · 13 glasses | 3.6 L · 14 glasses | 4.2 L · 17 glasses |
| 100 kg | 3.5 L · 14 glasses | 3.9 L · 16 glasses | 4.6 L · 18 glasses |
Computed with the same function as the calculator: 35 ml per kilo of body weight, adjusted for activity and climate, between 1.5 and 5 litres and rounded to 50 ml; 250 ml glasses. General water intake reference: EFSA (2010). These are reference ranges for healthy adults, not a diagnosis or individual advice.
FAQ
How much water should I drink a day at 60, 70 or 80 kg?
With little activity, about 2.1 L at 60 kg, 2.5 L at 70 kg and 2.8 L at 80 kg. If you exercise 3 to 5 days it rises to 2.4, 2.8 and 3.2 L, and with heat and a lot of activity to 2.8, 3.3 and 3.7 L. The two-litre rule is only an average.
How many glasses of water a day is that?
In 250 ml glasses, a fairly inactive 70 kg person needs about 10 a day, and a 60 kg person about 8. No need to count every one: coffee, tea, milk and the water in food count too.
Do coffee and tea count as water?
Yes. Despite the myth, the diuretic effect of caffeine at normal doses does not offset the fluid in the drink — the net contribution is positive. The same goes for tea, milk and soup. Alcohol is the genuine exception.
How do I know if I am drinking enough?
The simplest indicator is urine colour: pale yellow means well hydrated, dark yellow means drink more. Thirst is a reliable signal for most healthy adults, though it blunts with age, which is why older adults benefit from drinking on a schedule rather than on demand.
Can you drink too much water?
Yes, though it is rare. Drinking very large volumes in a short time can dilute blood sodium (hyponatraemia), which is dangerous. It shows up mostly in endurance events where people drink far beyond thirst. Spreading intake across the day avoids it entirely.
Keep reading
- How much water should you drink per day →
- Water retention: causes and solutions →
- Electrolytes and sports hydration →
- Satiating foods to avoid hunger →
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