Water Intake Calculator
This tool starts from 35 ml per kg of body weight. A 70 kg person with moderate activity in a temperate climate gets about 3.2 L (13.1 cups of 240 ml). It is a general guide, not medical advice.
How to use
- Enter your weight and choose kg or lb.
- Pick the activity level that matches a typical day, and choose Hot if you live or work in hot weather.
- Read the daily guide in milliliters or ounces, along with liters and 240 ml cups.
How it works
This calculator uses a common rule of thumb rather than a clinical formula: 35 ml of water per kilogram of body weight, plus a fixed amount for activity (0, 350, 700 or 1,000 ml) and 500 ml more in hot weather. The total is rounded to the nearest 10 ml.
For example, a 70 kg person with moderate activity in a temperate climate gets 70 x 35 = 2,450 ml plus 700 ml, or 3,150 ml (about 3.2 liters or 13 cups).
The figure counts all fluids, and food usually supplies a share of daily water as well. It is a general guide, not medical advice. Needs vary with health, diet, sweat rate and medication. If you are pregnant or breastfeeding, have kidney or heart disease, or take medicine that affects fluid balance, ask your doctor how much to drink.
Values used
| Factor | Amount |
|---|---|
| Base | 35 ml per kg of body weight |
| Sedentary (mostly sitting) | +0 ml |
| Light (light exercise 1 to 3 days a week) | +350 ml |
| Moderate (exercise 3 to 5 days a week) | +700 ml |
| Active (hard exercise or physical work most days) | +1,000 ml |
| Hot climate | +500 ml |
| 1 cup | 240 ml |
| 1 US fluid ounce | 29.57 ml |
Last reviewed 2026-10-13
FAQ
Is this the amount I must drink?
No. It is a rough guide based on a simple rule of thumb. Thirst, urine color and your doctor's advice are better signals for your own needs.
Does coffee or food count?
Most drinks, including tea and coffee, add to your fluid intake, and fruit, vegetables and soups contain water too. The guide is a total for all fluids, not plain water only.
Can drinking too much water be harmful?
Yes. Drinking very large amounts in a short time can lower blood sodium. Spread intake through the day and do not force down far more than you need.
Who should ask a doctor first?
People who are pregnant or breastfeeding, have kidney, heart or liver conditions, or take diuretics or other medicines that affect fluid balance should get advice from a doctor rather than rely on a general guide.
Is my data sent anywhere?
No. The calculation runs in your browser and nothing you enter is sent to a server.