CALCULATOR 09
Water Intake Calculator
Daily fluid needs from your weight, exercise and climate—in litres, glasses and an hourly plan.
Daily fluid
Enter your weight.
For general information only; not medical advice. Consult a qualified professional before making health decisions.
How this is calculated
Base: 35 ml × weight (kg) Exercise: + 350 ml per 30 min (pro-rated) Hot/humid: + 500 ml Pregnant: + 300 ml Breastfeeding: + 700 ml
This is total fluid from all drinks. Around 20% of daily water typically comes from food on top of this.
Glasses are 250 ml. The hourly schedule splits your total evenly across your waking hours.
Sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010), Scientific opinion on dietary reference values for water. EFSA Journal 8(3):1459.
About the water intake calculator
Why a weight-based estimate
Larger bodies lose more water through breathing, skin and urine, so fluid needs scale with body weight. A base of 35 ml per kg lands most adults in line with European Food Safety Authority reference values, which put adequate total water intake at about 2.0 litres a day for women and 2.5 litres for men, including water from food.
Read more about the Water Intake calculator
Exercise and heat
Sweat losses rise with exercise and hot or humid weather. The calculator adds 350 ml for every 30 minutes of exercise and 500 ml for a hot climate. Long or intense sessions in the heat can need far more; weighing yourself before and after training shows how much you lose—each kilogram lost is roughly a litre of fluid to replace.
Pregnancy and breastfeeding
EFSA recommends an extra 300 ml a day during pregnancy and 700 ml a day while breastfeeding, to cover the growing blood volume and the water in breast milk.
Knowing you're getting enough
Pale yellow urine and rarely feeling thirsty are good signs. All drinks count—water, milk, tea and coffee included—and so does water-rich food like fruit, vegetables, soups and dal. You don't need to force water beyond thirst unless you're exercising hard or it's very hot.
When to follow your doctor instead
People with kidney disease, heart failure or liver disease may need to limit fluids—follow your doctor's limits. Drinking very large amounts quickly, especially during endurance events, can dilute blood sodium dangerously.
Frequently asked questions
How much water should I drink a day?
A common estimate is about 35 ml per kg of body weight, plus extra for exercise and hot weather. For a 70 kg adult that's around 2.5 litres of fluid a day.
Do tea, coffee and milk count toward water intake?
Yes. All drinks count. Caffeine has a mild diuretic effect, but in moderate amounts tea and coffee still hydrate you overall.
Can you drink too much water?
Yes. Drinking very large amounts in a short time can cause hyponatremia (low blood sodium). Drink to thirst, and follow your doctor's limits if you have kidney, heart or liver conditions.
How much more water do I need when exercising?
Around 350 ml per 30 minutes is a reasonable baseline. In hot conditions or long sessions you may need more; weigh yourself before and after to see your sweat losses.