Moderate to vigorous activity that makes you sweat
| Baseline (35 ml per kg) | 2,450 ml |
| Exercise (350 ml per 30 min) | 350 ml |
| Hot climate | 0 ml |
A general guideline for fluids from all drinks, including tea and coffee. Food usually supplies about 20% of the water you take in, which gives an extra margin.
How to use the Water Intake Calculator
- 1Enter your body weight and choose kg or lb with the toggle.
- 2Enter the average number of minutes you exercise per day.
- 3Select your climate: temperate or cool, or hot or humid.
- 4Read your daily target in liters, plus the same amount in fluid ounces and glasses.
- 5Check the breakdown to see how much comes from the baseline, exercise and climate.
How the daily water estimate works
This calculator uses a simple, commonly cited rule of thumb rather than a medical formula. It starts with a baseline of about 35 ml of fluid per kilogram of body weight. It then adds about 350 ml for every 30 minutes of exercise to replace sweat losses, and a further 500 ml if you live in or are spending time in a hot or humid climate.
The result is a general guideline for healthy adults. It counts all drinks, including water, milk, tea and coffee. About 20% of the water most people take in comes from food, especially fruit, vegetables, soups and other foods with a high water content, so a typical diet adds a margin on top of the figure shown.
Example calculations
A person weighing 70 kg who exercises for 30 minutes a day in a temperate climate gets a baseline of 70 × 35 = 2,450 ml, plus 350 ml for exercise, for a total of 2,800 ml. That is 2.8 liters, about 95 US fluid ounces or just over 11 glasses of 250 ml.
Someone weighing 80 kg who trains for 60 minutes in hot weather needs 2,800 ml as a baseline, 700 ml for exercise and 500 ml for the heat, or 4.0 liters in total. That is about 135 fluid ounces or 16 glasses. If you weigh yourself in pounds, the calculator converts automatically; 150 lb is about 68 kg, which gives a baseline of roughly 2.4 liters.
Signs you are drinking enough
Thirst is a reliable guide for most healthy people, and pale yellow urine usually means you are well hydrated. Dark urine, headaches, tiredness and dizziness can be signs that you need more fluid, especially after exercise or time in the heat. A quick weigh-in before and after a workout shows how much you sweated: each kilogram lost is about a liter of fluid.
Spreading drinks through the day is easier than catching up in one go. Keep a bottle nearby, drink with each meal and have a glass before and after exercise. Your energy needs and fluid needs often rise together, and the calorie calculator can estimate how much food you need for your activity level.
When you may need more or less
Needs rise during illness with fever, vomiting or diarrhea, at high altitude, and during pregnancy and breastfeeding. Long endurance events may also call for electrolytes, not just water. On the other hand, people with heart or kidney conditions are sometimes advised to limit fluids, so follow your doctor's guidance if that applies to you.
Drinking far more than you need is rarely a problem for healthy people, but very large volumes in a short time can dilute blood sodium, a condition called hyponatremia. Aim for steady intake rather than forcing down extra liters. For other quick health estimates, browse our health calculators.
Frequently asked questions
How much water should I drink a day?
A common guideline is about 35 ml per kilogram of body weight, which works out to roughly 2 to 3 liters for many adults, with more for exercise and hot weather. Use the calculator above for a figure based on your own weight and routine.
Do tea and coffee count toward my water intake?
Yes. Although caffeine has a mild diuretic effect, regular tea and coffee drinkers still retain most of the fluid. Plain water is still the best everyday choice because it has no sugar or calories.
Does food count toward hydration?
Yes. Roughly 20% of the water people take in comes from food. Fruits and vegetables such as cucumber, watermelon and lettuce are more than 90% water.
Is the 8 glasses a day rule correct?
Eight glasses of 250 ml is 2 liters, which is a reasonable minimum for many adults but too little for larger or very active people. A weight-based estimate is more personal than a single number for everyone.
How do I convert liters to ounces?
One liter is about 33.8 US fluid ounces, and one US fluid ounce is about 29.57 ml. The calculator shows both units. For body weight in other units, the weight converter converts between kilograms, pounds and stone.