Water Intake Tracker
Estimate a daily water intake target and glasses per day.
How much water you need in a day
Water needs scale with body size and with how much you sweat, which is why a single '8 glasses a day' rule fits almost nobody well. This water intake calculator starts from your body weight, then adjusts for activity, and returns a daily target in both litres and standard glasses so you can actually track it.
How to use the Water Intake Calculator
- Enter your Weight (kg).
- Choose an Activity Multiplier that matches your typical day.
- Read the target in litres and in 250 ml glasses.
- Add more on hot days, at altitude, or when you are ill.
Formula and a worked example
Litres = weight (kg) × 0.033 × activity multiplier
The 0.033 works out to roughly 33 ml per kilogram, which lines up with common clinical guidance. Food contributes about 20% of total fluid intake, so the figure here is drinking water rather than everything combined.
Worked example
A 70 kg person with light activity needs about 2.3 litres, or roughly 9 glasses. Training hard pushes the same person past 3 litres.
Frequently asked questions
Is eight glasses a day correct?
It is a rough average for an average adult. A 55 kg office worker needs noticeably less than a 95 kg labourer, which is why weight-based targets work better.
Do tea and coffee count?
Yes. Moderate caffeine is mildly diuretic but the fluid still counts towards your intake.
How can I tell if I am drinking enough?
Pale straw-coloured urine and infrequent thirst are the practical signs. Dark urine suggests you need more.
Can I drink too much water?
Rarely, but yes — very large volumes in a short time can dilute blood sodium dangerously. Spread intake across the day.
Related calculators
Other tools people use alongside the water intake calculator.