💧 Hydration Updated2026-07-18
Water Intake Calculator.
⚡
Quick answer
A good estimate is about 33 ml of fluid per kg of body weight, roughly 2.3 litres for a 70 kg adult, plus ~350 ml per 30 minutes of exercise and more in heat. Enter your details below for a personalised target in litres and glasses.
💧
Daily Water Intake
Recommended
2.7 L
11
glasses
(250 ml)
(250 ml)
11
cups
(240 ml)
(240 ml)
90
fl oz
✨ Live · Estimate from body weight (~33 ml/kg) plus activity and climate. Food gives ~20% of your fluid too. Drink to thirst; ask a doctor if you have kidney or heart conditions.
📊 Quick reference
Baseline water need by weight.
Temperate climate with light daily activity. Add more on hot days and after exercise.
| Body weight | Water / day | Glasses (250 ml) |
|---|---|---|
| 50 kg | 2.0 L | 8 |
| 60 kg | 2.3 L | 9 |
| 70 kg | 2.7 L | 11 |
| 80 kg | 3.0 L | 12 |
| 90 kg | 3.3 L | 13 |
| 100 kg | 3.7 L | 15 |
❓ FAQ
Common questions.
How much water should I drink a day?
A practical estimate is about 30–35 ml of fluid per kilogram of body weight, before adjusting for exercise and heat. For a 70 kg adult that's roughly 2.3 litres a day from all fluids. The old "8 glasses (2 litres)" rule is a reasonable average for many people, but a lighter or heavier person needs proportionally less or more. This calculator scales the figure to you.
Does exercise change how much water I need?
Yes. You lose fluid through sweat, so active days need more. A common guideline is an extra 350–500 ml for every 30 minutes of exercise, and more in heat. This calculator adds roughly 350 ml per 30 minutes of activity you enter. For long or intense sessions, also replace electrolytes (sodium, potassium), not just water.
Do coffee, tea and food count toward my water intake?
Yes. All beverages, including tea and coffee, count toward hydration; the mild diuretic effect of caffeine at normal amounts doesn't cancel out the fluid. Food contributes too, supplying about 20% of most people's water through fruit, vegetables, soups and other moist foods. The target here refers to total fluid, so you don't need to drink it all as plain water.
Can you drink too much water?
Rarely, but yes. Drinking a very large amount in a short time can dilute blood sodium (hyponatraemia), which is dangerous. This is mostly a risk for endurance athletes over-drinking during events, or certain medical conditions. For everyday life, spreading fluids through the day and drinking to thirst keeps you safe. If you have kidney, heart or liver conditions, follow your doctor's fluid advice over any calculator.
How do I know if I'm drinking enough?
The simplest check is urine colour: pale straw yellow usually means well hydrated, while dark yellow suggests you need more. Thirst, dry mouth, headaches and tiredness can be early signs of mild dehydration. Your needs rise in hot weather, at altitude, when ill with fever, and during pregnancy or breastfeeding.