Water Intake Calculator
How much water to drink a day for your weight and activity.
Optional. Total active minutes per day; leave at 0 if none.
Daily water target
- Millilitres
- 2,660 ml
- Litres
- 2.66 L
- Cups (250 ml)
- 10.6
- From body weight
- 2,310 ml
- From exercise
- 350 ml
A general wellness estimate, not medical advice. Your real needs shift with climate, diet, pregnancy, illness, and exercise. Food and other drinks count toward your total.
How the water intake calculator works
This tool estimates how much total fluid to aim for in a day, scaled to two things that genuinely move the number: your body weight and how much you exercise. Heavier bodies hold and lose more water, and activity adds losses through sweat and breathing, so a fixed “eight glasses” rule serves almost no one well.
The estimate has two parts. The baseline is your body weight multiplied by 33 ml per kilogram, which covers your everyday losses through urine, skin, and respiration. The activity bonus adds about 350 ml for every 30 minutes of exercise, prorated, so 15 minutes adds 175 ml and 45 minutes adds 525 ml. Adding the two gives your daily target:
total(ml) = weight(kg) * 33 + (exercise minutes / 30) * 350
The result is shown three ways that all describe the same volume: millilitres, litres (millilitres divided by 1,000), and standard cups of 250 ml (millilitres divided by 250). If you enter pounds, the calculator first converts to kilograms using the exact factor 1 lb = 0.45359237 kg, so both unit systems land on the same answer. Choosing imperial also reports the headline figure in US fluid ounces.
Worked example
Take someone who weighs 70 kg and does 30 minutes of exercise a day.
- Baseline:
70 * 33 = 2,310 ml - Activity bonus:
(30 / 30) * 350 = 350 ml - Total:
2,310 + 350 = 2,660 ml
That is 2.66 litres, or about 10.6 cups of 250 ml. With no exercise at all, the same person needs just the baseline of 2,310 ml, which is 2.31 litres or roughly 9.2 cups. Push the workout to a full hour and the activity bonus doubles to 700 ml, lifting the target to 3,010 ml, about 3.01 litres or 12 cups.
The same 70 kg in imperial is about 154 lb, and the calculator converts it back to 70 kg before applying the formula, so the answer is identical.
How to use it
- Pick your unit system, then enter your body weight.
- Enter your daily exercise in minutes. Leave it at 0 if you are resting; the field is optional and never required.
- Read your target as litres or fluid ounces, then use the cups figure as an easy way to track progress through the day.
- Switch units at any time. The calculator reconverts your weight, so you never have to do the arithmetic yourself.
Limitations
This is a general wellness estimate, not medical advice. The 33 ml per kilogram and 350 ml per half hour figures are practical rules of thumb, not a clinical prescription, and they cannot capture heat, humidity, altitude, illness, fever, pregnancy, or the fluid limits some heart and kidney conditions require. Food and other drinks count toward the total, so you will rarely need to drink the whole figure as plain water. Let thirst and urine colour guide you day to day, and defer to your clinician’s advice if you have any condition that affects how your body handles fluid.
Frequently asked questions
How much water should I drink a day?
There is no single number that fits everyone, which is why this tool scales the estimate to your body weight and how much you move. As a starting point it uses about 33 ml of water per kilogram of body weight, then adds roughly 350 ml for every 30 minutes of exercise to replace what you lose through sweat and breathing. Treat the result as a sensible target to aim for across the day, not a strict quota.
Does food and other drinks count toward the total?
Yes. Most people get a meaningful share of their fluid from food, especially fruit, vegetables, soups, and dairy, and from drinks like tea, coffee, and milk. The figure this calculator gives is total fluid for the day, so you do not need to drink all of it as plain water. If you eat a lot of water-rich food you will reach the target with less drinking.
Why does exercise increase the amount?
When you exercise you lose water through sweat and faster breathing, and that loss has to be replaced to keep your blood volume and temperature regulation working. The tool adds about 350 ml for each 30 active minutes as a simple way to account for that. Long sessions, heat, and heavy sweating push the real figure higher, so use the number as a floor on hard training days.
Can I drink too much water?
Yes, although it is uncommon. Drinking very large volumes in a short time can dilute the sodium in your blood, a condition called hyponatraemia that is dangerous in extreme cases. Spread your intake across the day rather than forcing large amounts at once, and let thirst and the colour of your urine guide you. Pale straw usually means you are well hydrated.
Is this estimate right for everyone?
No. It is a general wellness guide for healthy adults. Pregnancy and breastfeeding raise fluid needs, hot or dry climates raise them further, and some heart, kidney, and liver conditions require a fluid limit set by a doctor. Children and older adults also have different needs. If you have a medical condition that affects fluid balance, follow your clinician's advice over any calculator.