Water Intake Calculator

1. Choose your weight units and activity level.
2. Enter your body weight.
3. Optionally add daily exercise minutes.
4. Read your daily water target in litres, cups and fluid ounces.

Here is what each result means:

A daily water target is a rough guide to how much water to drink to stay well hydrated. Water makes up more than half of your body and is needed for almost every process, from regulating temperature to carrying nutrients and removing waste. Drinking enough helps energy, concentration and digestion.

A widely used rule of thumb is about 35 millilitres of water per kilogram of body weight, so a heavier person needs more. Activity raises the target because you lose water through sweat and faster breathing, and hot weather increases it further. This calculator starts from your weight, adjusts for your activity level and adds an allowance for exercise.

The result is a starting point, not a strict rule. Around 20 percent of your fluid usually comes from food, and other drinks count too, so you do not need to hit the full figure from plain water alone. Thirst and the colour of your urine, pale straw is ideal, are good everyday guides to whether you are drinking enough.

It scales your weight by a per-kilogram guide, adjusts for activity and adds exercise.

1. Multiply your weight in kilograms by about 35 millilitres.
2. Apply an activity factor: 1.0 sedentary, 1.1 moderate, 1.2 active.
3. Add about 350 millilitres for every 30 minutes of exercise.

Hydration works with nutrition; see the protein intake calculator and the BMI calculator.

A moderately active adult weighs 70 kilograms.

Calculation: 35 millilitres times 70 kilograms is 2,450 millilitres. A moderate activity factor of 1.1 raises it to about 2.7 litres, or roughly 11 cups a day. Adding 30 minutes of exercise would add about another 350 millilitres.

The more active you are, the more water you lose and need to replace.

On top of the activity factor, the calculator adds water for the specific minutes of exercise you enter, since a hard workout can lose a litre or more of sweat in an hour. In hot or humid conditions you may need even more than these guides suggest.

The same target can be shown in several everyday units.

The old advice of eight 8-ounce glasses a day comes to about 1.9 litres, which suits a lighter, less active person. Scaling by weight and activity, as this calculator does, gives a more personal target than a single fixed number for everyone.

Body Weight

A larger body needs more water, so the target scales with your weight.

Activity and Exercise

Sweat and faster breathing lose water, so more activity raises the target.

Climate and Health

Heat, humidity, illness, pregnancy and breastfeeding all increase how much you need.

Building a Habit

Set a clear daily target to work toward if you tend to forget to drink.

Training and Sport

Plan hydration around workouts and hot-weather activity.

General Wellbeing

Check whether your usual intake is roughly in the right range.

1. Forgetting Food and Other Drinks

About a fifth of your fluid comes from food, and other drinks count too, so you need less plain water than the total.

2. Ignoring Climate

Hot or humid weather raises your needs well above a baseline figure.

3. Drinking Far Too Much

Very large amounts in a short time can be harmful. Spread water through the day.

4. Using the Wrong Weight Unit

Set the toggle to match whether you enter kilograms or pounds.

5. Treating It as Exact

It is a guide. Thirst and urine colour are useful day-to-day checks.

The estimate is a general guide based on common hydration rules, not a medical prescription.

A common guide is about 35 millilitres per kilogram of body weight, adjusted for activity. A moderately active 70 kilogram adult needs roughly 2.7 litres, or about 11 cups.

Multiply your weight in kilograms by about 35 millilitres, apply an activity factor, and add around 350 millilitres for every 30 minutes of exercise.

Eight 8-ounce glasses is about 1.9 litres, which suits a lighter, less active person. Scaling by weight and activity gives a more personal target.

Yes. About 20 percent of your fluid usually comes from food, and other drinks count too, so you do not need the whole target from plain water.

Yes. Exercise loses water through sweat, so add extra. This calculator adds about 350 millilitres for each 30 minutes of exercise.

Yes. Drinking very large amounts in a short time can dangerously dilute your blood sodium. Spread your intake through the day rather than all at once.

Pale straw-coloured urine and infrequent thirst are good signs. Dark urine or frequent thirst suggests you need to drink more.

Yes. Set the weight toggle to pounds and enter your weight; the calculator converts it to kilograms internally.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Water and hydration (Wikipedia).
• Body water (Wikipedia).
• Water: how much should you drink (Mayo Clinic).