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 applies a body-weight and exercise rule of thumb to produce a fluid scenario for a healthy adult. The formula is not a Dietary Reference Intake and is not a clinical prescription. Actual needs vary with age, sex, pregnancy or breastfeeding, food, activity, environment, illness, and health conditions.
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
The model returns 2.66 litres, or about 10.6 cups of 250 ml. With no entered exercise it returns 2.31 litres; with one hour it returns 3.01 litres. These values describe the formula’s output and should not be read as measured individual requirements.
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/kg baseline and exercise adjustment are informal assumptions. Total water includes moisture in food and beverages, so the output is not a plain-water requirement. Needs can rise with heat, activity, fever, vomiting, or diarrhea, while some heart, kidney, liver, and endocrine conditions require clinician-directed fluid limits. Excessive intake can also be dangerous. Follow medical guidance when fluid balance is affected.
Sources and scope
- Jurisdiction
- General educational rule of thumb for healthy adults
- Data current to
- July 30, 2026
- Last updated
- About Water and Healthier Drinks — Centers for Disease Control and Prevention
- Dietary Reference Intakes for Water — National Academies of Sciences, Engineering, and Medicine
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.