Water Intake Calculator by Weight
Calculate your recommended daily water intake based on body weight. Adjust for exercise and climate.
How to use this tool
- Enter your body weight in kilograms.
- Enter your average daily exercise time in minutes.
- See your recommended daily water intake in litres and glasses.
Get a personalised daily water intake recommendation based on your body weight and activity level.
Formula
Base intake (L) = weight_kg × 35 ÷ 1000
Exercise extra (L) = (exercise_min ÷ 30) × 0.35
Total daily water (L) = base + extra
Glasses = ⌈ total ÷ 0.25 ⌉
How it works
This calculator estimates daily water needs using a widely cited rule of 35 mL per kilogram of body weight as a baseline, then adds 350 mL for every 30 minutes of exercise to account for sweat losses. The glass count is derived by dividing the total by 250 mL (a standard cup) and rounding up. This is a general guideline; actual needs vary with climate, diet, health status, and individual physiology.
Worked example
Worked example
- Body weight = 70 kg, Exercise = 30 min/day
- Base intake = 70 × 35 ÷ 1000 = 2.45 L
- Exercise extra = (30 ÷ 30) × 0.35 = 0.35 L
- Total = 2.45 + 0.35 = 2.8 L
- Glasses = ⌈ 2.8 ÷ 0.25 ⌉ = ⌈ 11.2 ⌉ = 12 glasses
Recommended daily water: 2.8 L (12 glasses of 250 mL)
Key terms
- Daily water intake
- The total fluid a person should consume in a day from all sources, including drinks and water-rich foods, to maintain hydration.
- 35 mL/kg rule
- A common clinical guideline recommending approximately 35 mL of water per kilogram of body weight per day for healthy adults.
- MET-adjusted hydration
- An increase in fluid intake recommended to replace water lost through sweat during physical activity, typically around 300–500 mL per 30 minutes of moderate exercise.
- Ceiling function (⌈ ⌉)
- A mathematical operation that rounds a number up to the nearest whole integer, used here to ensure a full glass is counted for any partial remainder.
Frequently asked questions
- How much water should I drink per day?
- A common rule of thumb is 35 mL per kilogram of body weight, plus extra for exercise. A 70 kg person doing 30 minutes of exercise should aim for about 2.8 litres per day.
- Does coffee count toward daily water intake?
- Caffeinated drinks have a mild diuretic effect but still contribute to hydration. Plain water is best; other fluids count partially.