Daily water intake calculator
Find out how many liters of water to drink per day based on your weight and activity.
General reference (35–45 ml per kg). Hot weather, pregnancy and some conditions increase the need.
How the calculation works
The estimate starts from a simple, widely used reference: an amount of water proportional to body weight.
water (ml) = weight (kg) × ml per kg
- 35 ml/kg — light activity (desk routine, little exercise)
- 40 ml/kg — moderate activity (regular exercise)
- 45 ml/kg — intense activity (long training, physical work)
Step-by-step example (70 kg, light activity)
70 × 35 = 2,450 ml ≈ 2.45 liters per day, about ten 250 ml glasses.
Is this only plain water?
No. Part of your hydration comes from food (fruit, soups, salads) and other drinks. Treat the number as a practical fluid target, spread across the day.
When to drink more
Heat and humidity, fever, diarrhea or vomiting, breastfeeding, pregnancy and altitude all raise the need. Urine color is a good gauge: pale yellow usually means well hydrated; dark yellow suggests drinking more.
Examples
- 60 kg, light activity: 60 × 35 = 2,100 ml ≈ 2.1 L/day (~8 glasses).
- 80 kg, intense activity: 80 × 45 = 3,600 ml ≈ 3.6 L/day.
Frequently asked questions
Do coffee and tea count?
They contribute to hydration, but plain water should be the base. Coffee's diuretic effect at normal doses is small.
Can drinking too much water be harmful?
In extreme amounts over a short period, yes (hyponatremia, when blood sodium gets too diluted). For most people this is rare; the body eliminates the excess.
Is the "8 glasses a day" rule valid?
It is an easy shortcut (≈2 L), but ignores weight and activity. The per-kg estimate is more personalized.
Do coffee and tea count as hydration?
Yes. At moderate intake the fluid volume outweighs caffeine's mild diuretic effect. Alcohol is different.
Is urine colour reliable?
It is a good practical indicator, except that B-complex supplements turn urine bright yellow regardless of hydration.
Can I drink too much water?
Yes. Excessive intake in a short time can cause hyponatremia. It is rare day to day but happens in long endurance events.
How much extra should I drink when training?
About 500–700 ml per hour, more in heat. Weighing before and after training calibrates it: each kilo lost is roughly 1 litre to replace.
Sources and references
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Updated on June 18, 2026 · by Rafael Rossi · Methodology & sources