How much water should you drink? This free water intake calculator estimates your daily needs from your weight, activity and climate, shown in litres, cups and fluid ounces.
About you
min
A weight-based estimate of total daily water. Around 20% of your water usually comes from food, so the rest is from drinks. Thirst and pale urine are good everyday guides.
Estimated daily water
— litres/day
Enter your weight
Millilitres
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Cups (240 ml)
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Fluid ounces
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From drinks (~80%)
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A general estimate — real needs vary with body size, activity, climate, pregnancy and health. Some conditions require fluid limits; if a doctor has advised one, follow that instead. Drinking to thirst suits most healthy people.
Use this free water intake calculator to estimate how much water you need each day. Enter your weight, add any exercise and your climate to see your daily target in litres, cups and fluid ounces.
What this water intake calculator shows you
A water intake calculator estimates your daily water needs from your body weight, adjusted for exercise and climate. It shows your total in litres, millilitres, cups and fluid ounces — plus roughly how much should come from drinks, since about 20% of your water comes from food.
How much water should I drink a day?
A common estimate is around 30–35 ml of water per kilogram of body weight. For a 70 kg person that’s roughly 2.5 litres, rising with exercise and hot weather. The old “8 cups a day” rule is a reasonable ballpark for many adults, but real needs vary a lot.
What affects your water needs
Body size — larger bodies generally need more.
Activity — you lose fluid through sweat, so exercise raises needs.
Climate — hot or humid weather increases losses.
Pregnancy, breastfeeding and some illnesses change requirements.
How to use the water intake calculator
Enter your weight (tap the unit to switch kg/lb).
Add today’s exercise in minutes.
Choose your climate.
Read your estimate in litres, cups and ounces.
Tips for staying hydrated
Drink to thirst — it’s a reliable guide for most healthy people.
Check your urine — pale straw usually means well hydrated.
Spread it out across the day rather than all at once.
Foods count too — fruit, vegetables and soups add fluid.
Can you drink too much water?
Rarely, but yes — drinking very large amounts in a short time can dilute blood sodium (hyponatraemia), which is dangerous. For most people this isn’t a concern, but don’t force huge volumes. If a doctor has set you a fluid limit, follow that instead of a general estimate.
Water Intake FAQ
How much water should I drink a day?
A common estimate is about 30–35 ml per kilogram of body weight — roughly 2.5 litres for a 70 kg person — rising with exercise and hot weather. The "8 cups a day" rule is a reasonable ballpark, but needs vary.
How is my water intake calculated?
This tool uses about 35 ml per kilogram of body weight as a baseline, adds roughly 350 ml per 30 minutes of exercise, and increases the total in hot or humid climates.
Does food count toward water intake?
Yes. Around 20% of your water typically comes from food, especially fruit, vegetables and soups, so not all of your total needs to come from drinks.
How do I know if I'm drinking enough?
Thirst is a good guide for most healthy people, and pale straw-coloured urine usually signals good hydration. Darker urine suggests you should drink more.
Can you drink too much water?
Rarely, but drinking very large amounts quickly can dangerously dilute blood sodium. For most people this isn't a concern — just don't force huge volumes, and follow any fluid limit your doctor has set.
Is the water intake calculator free to use?
Yes, this water intake calculator is completely free, needs no sign-up, and gives instant results in your browser.
