Water Intake by Body Weight
Calculate exactly how much water you should drink per day based on your body weight, with adjustments for exercise and climate.
The simplest body-weight-based hydration formula: 33 ml of water per kg of body weight at sedentary baseline. A 70 kg person sitting in a cool office needs about 2.3 litres. The same person doing a 30-minute gym session needs another 500 ml on top.
Water Per Kilogram Table
| Body weight | Sedentary baseline | + 30 min exercise | + Hot climate |
|---|---|---|---|
| 50 kg | 1.65 L | 2.15 L | 2.5 L |
| 60 kg | 2.0 L | 2.5 L | 2.9 L |
| 70 kg | 2.3 L | 2.8 L | 3.2 L |
| 80 kg | 2.65 L | 3.15 L | 3.6 L |
| 90 kg | 3.0 L | 3.5 L | 4.0 L |
| 100 kg | 3.3 L | 3.8 L | 4.4 L |
Where the 33 ml/kg Comes From
The number is a sports-nutrition rule of thumb derived from older balance studies. The US Institute of Medicine recommends 2.7 L total water per day for women and 3.7 L for men. Roughly 20% of that comes from food (fruits and vegetables contain 80-95% water), and 80% from beverages.
Adjustments by Climate
- Cool / AC: subtract 8%
- Moderate: baseline
- Hot / humid: add 15-20%
Use the Full Calculator
The Water Intake Calculator handles every scenario described on this page. For the deeper math and worked examples, read the companion guide.