How Much Water Should You Drink a Day?
The weight-based formula, adjustments for exercise and heat, and the signals that beat any schedule.
3 min read
Step by step
- Start with 30–35 ml per kilogram of body weight per day.
- Add 350–700 ml per 30 minutes of exercise.
- Increase further in hot or humid climates.
- Check urine color — pale yellow means you are on track.
Key takeaway: About 30–35 ml per kg, adjusted for sweat and heat.
The weight-based starting point
A common clinical starting point is 30–35 ml of water per kilogram of body weight per day. A 70 kg adult lands near 2.1–2.45 litres — close to the familiar 'eight glasses' advice, but scaled to the person.
This covers total water, including the roughly 20% that comes from food, so the drinking target is a little lower than the headline number.
Adjusting for exercise and climate
Add roughly 350–700 ml for every 30 minutes of exercise, scaled by intensity and sweat rate. Hot or humid climates, fever, and high altitude all raise needs further.
The calculator applies these adjustments for you: enter weight, activity minutes and climate and it produces a single daily target.
Signals beat schedules
Pale-yellow urine and rarely feeling thirsty are better day-to-day indicators than hitting an exact number. Dark urine, headaches and dry mouth suggest you are behind.
More is not always better: drinking far beyond thirst can dilute blood sodium (hyponatremia), a real risk for endurance athletes who force fluids.
Do it automatically
Recommended daily water based on weight, activity and climate.
Open the Water Intake Calculator