Water Intake
WEBWork out how much water to drink each day from your weight and activity.
This is a general guide, not medical advice. Your needs change with health, pregnancy and medication — ask a professional if unsure.
What is the Water Intake tool?
This water intake calculator works out how much water you should drink each day and shows the target three ways: liters, US fluid ounces, and standard 250 ml cups. It starts from your body weight using the widely quoted rule of about 35 ml of water per kilogram, then adds an allowance for how active you are and for how hot your climate is — the two things that push your daily needs up the most. Enter your weight in kilograms or pounds, pick an activity level and a climate, and the recommendation updates instantly.
Bigger bodies, harder training and hotter weather all raise how much fluid you lose through sweat and breathing, so the calculator adds a bonus for high activity and for warm or hot climates on top of the weight baseline. The result is a sensible daily goal you can split across the day — a good habit is a glass when you wake up, one with each meal, and a few between. Roughly a third of your fluid also comes from food, so treat the number as a drinking target for a normal diet rather than an exact quota.
Everything runs entirely in your browser: your weight and choices are never uploaded, no account is needed, and the tool works offline once the page has loaded. It is free with no limits. One honest caveat — this is a general guideline, not medical advice. Your real needs shift with health conditions, pregnancy and breastfeeding, some medicines, illness and altitude, so if you are unsure, or you have a kidney or heart condition, check the target with a health professional.
How to use the Water Intake
- Choose metric (kg) or imperial (lb) and enter your body weight.
- Pick your activity level — low, moderate or high.
- Pick your climate — temperate, warm or hot.
- Read your recommended daily water in liters, plus the ounces and cups equivalents.
- Spread it across the day: a glass on waking, one with each meal, and sips in between.
Frequently asked questions
How much water should I drink a day?
A common starting point is about 35 ml of water per kilogram of body weight, so around 2.4 liters for a 70 kg adult. Add roughly 0.3–0.7 liters if you train hard or live in a hot climate. This calculator does that math for you and shows the target in liters, ounces and cups.
Is the '8 glasses a day' rule accurate?
Eight 250 ml glasses is about 2 liters — a fine rough guide for an average adult, but it ignores your size, activity and climate. A weight-based estimate like this one is more personal: a larger or more active person in a hot place needs noticeably more than eight glasses.
Does coffee, tea or food count toward my water?
Yes. Tea, coffee, milk and most drinks hydrate you, and about a third of your fluid typically comes from food such as fruit, vegetables and soup. Treat this number as a total daily fluid target for a normal diet, not only plain water.
Should I drink more when it is hot or when I exercise?
Yes — both make you lose more water through sweat, which is why the calculator adds a bonus for high activity and for warm or hot climates. On very hot days or during long workouts, drink to thirst and top up before, during and after.
Can I drink too much water?
It is rare but possible: drinking far more than you need in a short time can dilute the sodium in your blood (hyponatremia). Spread your intake through the day and use the calculator's number as a goal, not a minimum to hit in one sitting.
Is my data private, and is this free?
Yes to both. Your weight and choices are processed entirely in your browser — nothing is uploaded, stored or sent to a server — and the tool is free with no sign-up and no limits. It even works offline once the page has loaded.