Water Intake Calculator
A common guide is 33 ml of water per kg of body weight a day, plus about 350 ml for every 30 minutes of exercise and more in hot weather. A 70 kg adult who exercises for 45 minutes in a mild climate needs about 2.8 litres a day, or 11 glasses of 250 ml.
33 ml per kg of body weight, plus 350 ml per 30 minutes of exercise and 500 ml in hot weather.
How to use the Water Intake Calculator
- Enter your body weight in kg or lb.
- Enter how many minutes you exercise on a typical day.
- Choose a mild or hot climate.
- Read your daily water target in litres, 250 ml glasses and US fluid ounces.
Formula
Water (L) = 0.033 × weight (kg) + 0.35 × (exercise minutes ÷ 30) + 0.5 if hotThe baseline of 33 ml per kg is adjusted for sweat lost during exercise and in hot weather. The result covers all fluids, including drinks other than water.
Signs of good hydration
- Pale yellow urine.
- Little or no thirst.
- Urinating every 3 to 4 hours during the day.
- Dark urine, headache, dizziness and fatigue can signal dehydration.
What counts toward your intake
Water, milk, tea, coffee and other drinks all count, and roughly 20% of daily fluid comes from food such as fruit, vegetables and soups. Coffee and tea have a mild diuretic effect but still provide net hydration in normal amounts. Alcohol does not help hydration.
When to get personal advice
People with kidney, heart or liver conditions, those on diuretics, and pregnant or breastfeeding women should follow their doctor's advice, as some conditions require more fluid and others require less.
Water Intake Calculator questions
How much water should I drink per day?
A practical guide is about 33 ml per kg of body weight, which is about 2.3 litres for a 70 kg adult, plus more for exercise and heat. Health authorities suggest total fluid intakes of around 2 litres a day for women and 2.5 litres for men, including fluid from food.
How much more water do I need when I exercise?
Add roughly 350 ml for every 30 minutes of exercise, and more in hot conditions or if you sweat heavily. Drink some water in the hours before training, sip during long sessions, and rehydrate afterwards. Weighing yourself before and after shows how much you lost.
Do coffee and tea count toward my water intake?
Yes. Caffeinated drinks have a mild diuretic effect, but in normal amounts they still add to your total fluid intake. Milk, herbal tea and water-rich foods count too. Alcohol is the exception, as it increases fluid loss.
How do I know if I am drinking enough?
The simplest check is urine colour: pale yellow means you are well hydrated, dark yellow means you need more. Other good signs are rarely feeling thirsty and urinating every few hours. Headaches, tiredness and dizziness can be early signs of dehydration.
Can I drink too much water?
Yes, though it is rare. Drinking very large amounts quickly can dilute blood sodium (hyponatremia), causing nausea, headache and confusion, and in severe cases seizures. Endurance athletes are most at risk and should replace electrolytes on long events.
How does hot weather change my water needs?
Heat and humidity increase sweating, so you may need 0.5 to 1 litre or more extra per day, and more again if you are active outdoors. High altitude also raises fluid loss through breathing. Drink regularly rather than waiting until you feel thirsty.
Do pregnant or breastfeeding women need more water?
Yes. Typical guidance is about 2.3 litres a day from drinks during pregnancy and about 3.1 litres while breastfeeding, on top of fluid from food. Needs vary, so follow advice from your midwife or doctor, especially in hot weather or if you have medical conditions.
What is the easiest way to track water intake?
Use a bottle with volume markings and refill it a set number of times, or log glasses in an app. Linking drinks to routines, such as a glass with each meal, makes the target easier to hit without constant tracking.