About the Water Intake Calculator
A free, instant daily hydration estimator based on body weight and activity level, with metric and imperial input and multiple output units.
What it is
The Water Intake Calculator estimates your daily fluid needs the moment you enter your weight and choose your activity level — no button to click, no page to reload. It accepts weight in kilograms or pounds and returns your estimate in litres, millilitres, cups, or fluid ounces, so you can work in whichever units make sense to you.
The estimate adjusts upward for more active lifestyles to account for the extra fluid you lose through sweat. Everything runs in your browser — your details are never sent to a server or stored anywhere.
Key features
Weight-based estimate
Your daily target is calculated from your body weight in kilograms, using a widely referenced ml-per-kg approach that scales naturally with body size.
Activity-level adjustment
Five activity levels — from sedentary to very active — adjust the estimate to account for extra fluid lost during exercise, giving you a more personalised figure than a flat recommendation.
Metric & imperial input
Enter your weight in kilograms or pounds. The tool converts internally so the result is identical whichever unit system you choose.
Multiple output units
See your daily target in litres, millilitres, US cups, or US fluid ounces — all four conversions are shown at once so you can use whatever unit fits your bottles or habits.
How the estimate is calculated
The base formula is: daily water (ml) = body weight (kg) × ml per kg, where the ml-per-kg multiplier increases with activity level:
Sedentary — 30 ml/kg
Little or no exercise; mostly desk-based work.
Lightly active — 35 ml/kg
Light exercise or sport 1–3 days per week.
Moderately active — 40 ml/kg
Moderate exercise or sport 3–5 days per week.
Active — 45 ml/kg
Intense exercise or sport 6–7 days per week.
Very active — 50 ml/kg
Very hard exercise daily, or a physically demanding job.
Imperial weights are converted to kilograms before the calculation, so metric and imperial inputs produce the same result to within rounding.
A note on individual variation
This tool provides a general estimate and is not medical advice. Hydration needs vary with health, climate, activity, pregnancy, and individual factors. Consult a physician if you have any condition affecting your fluid intake or any health concerns.
Find your daily water target
Free, no sign-up required. Works on any device.
Open the Water Intake Calculator