Hydration Calculator
Estimate your daily water intake target based on your body weight and activity level, and track how much you've had so far today against that goal.
How it works
- Enter your weight and select your activity level on the setup screen.
- The tool sets a personalised daily water target in millilitres.
- Tap the quick-log buttons every time you drink — a glass, a bottle, or a custom amount.
- The ring on the home screen fills as you log, resetting automatically at midnight.
How your daily target is calculated
The target starts with body weight at 35 ml of water per kilogram, then adds amounts for the things that increase fluid loss. Each 30 minutes of daily activity adds 350 ml, a hot climate adds 500 ml, pregnancy adds 300 ml and breastfeeding adds 700 ml. If you work in pounds and fluid ounces the tool converts at the edges (1 lb = 0.4536 kg, 1 US fl oz = 29.57 ml), so the target is the same in either system, and it is rounded to the nearest 10 ml, since a target is not precise to the millilitre.
For example, someone who weighs 70 kg and exercises for 60 minutes a day in a normal climate has a target of 70 x 35 = 2,450 ml, plus 2 x 350 = 700 ml for activity, which is 3,150 ml. In a hot climate the same person would add 500 ml for a target of 3,650 ml.
How this compares with official guidance
The multipliers in this tool are practical rules of thumb and not clinical values, so treat the result as a starting point. For context, official reference figures for total water intake, including water from food (typically about a fifth of the total), are around 2.0 litres a day for women and 2.5 litres for men in European guidance, and about 2.7 and 3.7 litres in US guidance. Needs vary with body size, diet, temperature, altitude and health, so no single number is right for everyone.
Logging and sharing
After you set up your profile, the main screen shows a ring of today's progress. Use the quick buttons or enter an amount in millilitres to log each drink, and undo the last entry if you make a mistake. The log is stored on your device and nothing is uploaded. You can also share your target as a link; the link carries only the number, and a friend who opens it sees it as a suggestion before setting up their own.
When not to follow the number
Thirst, urine colour and how you feel are useful signals. A pale yellow colour usually means you are well hydrated. People with kidney, heart or liver conditions, or who take medicines that affect fluid balance, may be told to drink more or less than a general target, and should follow their doctor's advice. Drinking far more than you need is not helpful and in rare cases can be harmful, so this target is a guide to aim for, not a quota to force down.
Frequently asked questions
How is the daily water target calculated?
It scales from your body weight, with an added allowance for time spent exercising, since sweat increases fluid needs. It's a general guideline, not a medical prescription.
Does this count water from food and other drinks?
No — this tracks plain water intake specifically. Food and other beverages contribute meaningfully to hydration too, so this target is a floor, not the whole picture.
Sources and further reading
Formulas checked against the sources below. Last reviewed . General information only, not professional advice.