💧Water Intake Calculator
Estimate your daily water needs from your body weight and activity level. Works in metric or imperial units — see results in litres, millilitres, cups, or fluid ounces.
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.
Free Water Intake Calculator Online
Not sure how much water to drink each day? Our free Water Intake Calculator gives you a personalised estimate the moment you enter your details. As a fast and simple water intake calculator, it bases your daily target on your body weight and adjusts it for how active you are — so you get a figure that fits you rather than a generic "eight glasses" rule.
But it does more than one number. Work in metric or imperial units and see your estimate in litres, millilitres, cups, or fluid ounces, with a higher target on more active days when you lose more fluid through sweat. It also explains that hydration needs vary with climate, health, and individual factors, so you can treat the result as a helpful guide.
Simply enter your weight and activity level to see your estimate instantly. No sign-up, no downloads, no limits — just a clear guide whenever you need it. Learn more in the FAQ or About pages.
About the Water Intake Calculator
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
Frequently Asked Questions
How does the water intake calculator work?
Enter your body weight and activity level, and the tool estimates your daily water needs, adjusting the figure upward the more active you are — no button refresh needed.
Is this calculator free to use?
Yes, it's completely free with no sign-up, downloads, or limits. Use it as often as you like.
How is my water intake estimated?
The estimate is based on your body weight, then adjusted for your activity level to account for extra fluid lost through sweat during exercise. A sedentary person uses around 30 ml per kilogram of body weight per day as a starting point, rising to 50 ml per kilogram for very active individuals.
Can I use metric or imperial units?
Yes. You can enter your weight in kilograms or pounds and see your target in litres, millilitres, cups, or fluid ounces.
Does activity level really change how much I need?
Yes. More activity generally means more fluid lost through sweat, so active days typically call for more water than rest days.
Does food count toward my water intake?
Yes — many foods, especially fruits and vegetables, contribute to your total fluid intake, and other drinks count too. The estimate is for overall hydration, not water alone.
How accurate is the estimate?
It's a general guide, not a medical prescription. Actual needs vary with climate, temperature, health conditions, pregnancy, body size, and individual differences, so adjust to how you feel.
Is my data stored anywhere?
No. Your details are processed directly in your browser and are never stored or sent to a server, keeping your information completely private.
Does it work on mobile devices?
Yes, the calculator is fully responsive and works on smartphones, tablets, and desktops without any installation.
Can I drink too much water?
Yes — drinking extremely large amounts in a short time can be harmful. The estimate is a general daily guide; if you have specific health conditions or concerns about your fluid intake, speak with a doctor.