How Much Water Should You Drink a Day?
Updated June 2026
How much water to drink daily.
"Drink 8 glasses a day" is a rough rule that ignores your size and activity. Here's a better estimate based on your body weight.
The estimate
A common guideline is about 35 ml of water per kilogram of body weight (roughly half an ounce per pound):
Daily water (ml) ≈ weight in kg × 35
So a 70kg person needs about 2,450 ml — roughly 2.5 litres — before accounting for exercise.
Add for activity
Exercise and heat increase your needs. Add roughly 350–500 ml for every 30 minutes of intense activity, and more in hot weather.
What counts
- Water, of course — but tea, coffee and milk also contribute.
- Water-rich foods (fruit, soup, vegetables) add up too.
- Your body is good at signaling: drink to thirst, and check your urine is pale, not dark.
The calculator below turns your weight and exercise into a personalised daily target.
How much water to drink daily.
Frequently asked questions
Can you drink too much water?
Rarely, but yes — drinking extreme amounts in a short time can dilute blood sodium. For almost everyone, normal drinking to thirst is safe.
Does coffee dehydrate you?
Not meaningfully. The fluid in coffee and tea more than offsets their mild diuretic effect, so they still count toward hydration.