How much water should you drink a day?
A common evidence-based guideline is about 30–35 ml of water per kilogram of body weight, adjusted up for exercise and hot weather. This calculator uses ~35 ml/kg and adds extra for activity and climate.
How much water to drink by body weight
Daily water in litres using the calculator's method — about 35 ml per kg, scaled up for heat and topped up for exercise. Food provides some of this; tea, coffee and milk count too.
| Body weight | Baseline temperate, no exercise | +30 min exercise | +60 min exercise | Hot climate +60 min exercise |
|---|---|---|---|---|
| 45 kg (99 lb) | 1.6 L | 1.9 L | 2.3 L | 2.6 L |
| 50 kg (110 lb) | 1.8 L | 2.1 L | 2.5 L | 2.8 L |
| 55 kg (121 lb) | 1.9 L | 2.3 L | 2.6 L | 3 L |
| 60 kg (132 lb) | 2.1 L | 2.5 L | 2.8 L | 3.2 L |
| 65 kg (143 lb) | 2.3 L | 2.6 L | 3 L | 3.4 L |
| 70 kg (154 lb) | 2.5 L | 2.8 L | 3.2 L | 3.6 L |
| 75 kg (165 lb) | 2.6 L | 3 L | 3.3 L | 3.9 L |
| 80 kg (176 lb) | 2.8 L | 3.2 L | 3.5 L | 4.1 L |
| 85 kg (187 lb) | 3 L | 3.3 L | 3.7 L | 4.3 L |
| 90 kg (198 lb) | 3.2 L | 3.5 L | 3.9 L | 4.5 L |
| 95 kg (209 lb) | 3.3 L | 3.7 L | 4 L | 4.7 L |
| 100 kg (220 lb) | 3.5 L | 3.9 L | 4.2 L | 4.9 L |
| 110 kg (243 lb) | 3.9 L | 4.2 L | 4.6 L | 5.3 L |
| 120 kg (265 lb) | 4.2 L | 4.6 L | 4.9 L | 5.7 L |
Signs you may need more water
- Dark yellow urine (pale straw is the goal)
- Headaches, tiredness or difficulty concentrating
- Feeling thirsty — a sign you're already slightly dehydrated
How much water should I drink a day for my weight?
About 35 ml per kg as a baseline. That's 2.1 L at 60 kg, 2.5 L at 70 kg and 2.8 L at 80 kg — more if you exercise or it's hot.
How many glasses of water a day is that?
At 250 ml a glass, 2.5 litres is 10 glasses. The old "8 glasses a day" (2 litres) is a reasonable minimum for a smaller adult in a mild climate.
Does tea or coffee count?
Yes. Despite the myth, moderate caffeinated drinks still count toward your fluid intake for most people.
Can you drink too much water?
Rarely, but yes — drinking extreme amounts in a short time can dilute blood sodium. Spread intake across the day.