Water Intake Calculator
Estimate how much you should drink in a day from your weight, how much you exercise, the climate and, if it applies, pregnancy or breastfeeding. See the answer in litres, ounces and bottles, with a simple plan for spreading it through the day.
Your result
Enter your details above to see your daily water goal.
A general estimate for healthy adults, not medical advice. Your real needs depend on your health, diet, medicines and how much you sweat. Follow your doctor’s advice if you have a condition that affects fluid balance.
Why there is no single right answer
Ask five sources how much water you should drink and you will probably get five numbers. That is because the real answer depends on you. A small person sitting in a cool office loses much less fluid than a large person doing manual work in a hot climate. Sweat, breathing, urine and even the water in your food all feed into the balance.
This calculator does not pretend to settle the matter. It gives you a reasonable, transparent starting point built from the things that move the number most: your body weight, how much you exercise, how hot it is, and whether you are pregnant or breastfeeding. You can then adjust by how you feel and by what your urine colour tells you.
How to use this calculator
- Enter your weight in kilograms or pounds. Add your age if you like, since the calculator is for adults.
- Enter the minutes you exercise on a typical day and how hard, then choose your climate and life stage.
- Read your daily goal in litres, ounces and bottles, with a comfortable range either side.
- Open Daily plan options to set your wake-up time, bedtime and bottle size, and see how to spread the goal through the day.
How the estimate is built
Base = 30 ml × body weight in kg (kept between 1,500 and 3,500 ml)
Climate = base × 1.0 (temperate), 1.1 (warm) or 1.2 (hot)
Exercise = minutes × 6, 10 or 15 ml (light, moderate, vigorous)
Life stage = +300 ml (pregnant) or +700 ml (breastfeeding)
Daily goal = climate + exercise + life stage, rounded to 50 ml
The 30 ml per kilogram figure is a common rule of thumb for the fluids a healthy adult needs to drink on a quiet day. The exercise allowances reflect that people typically lose a few hundred millilitres to nearly a litre of sweat an hour depending on effort and heat. The pregnancy and breastfeeding additions follow the extra amounts suggested in European dietary guidance.
The comfortable range shown with your result is 10% either side of the goal. It is there because no formula can know your sweat rate, your diet or your day.
Worked examples
A quiet day
70 kg, no exercise, temperate climate. 70 × 30 = 2,100 ml, or 2.1 litres. That is about 71 US fluid ounces, or four and a bit 500 ml bottles.
A regular exerciser
The same person jogs for 45 minutes at a moderate effort. Exercise adds 45 × 10 = 450 ml, so the goal rises to 2,550 ml.
The same day in hot weather
Hot weather multiplies the base by 1.2, so 2,100 becomes 2,520, and adding the 450 ml for exercise gives 2,970, which rounds to about 2,950 ml.
During pregnancy
65 kg, no exercise, temperate climate. 65 × 30 = 1,950 ml, plus 300 ml for pregnancy is 2,250 ml.
Base amount by body weight
Before climate, exercise and life stage are added, this is the base amount from the formula above for a range of weights.
| Weight | Millilitres | Litres | US fl oz |
|---|---|---|---|
| 50 kg (110 lb) | 1,500 | 1.5 | 50.7 |
| 60 kg (132 lb) | 1,800 | 1.8 | 60.9 |
| 70 kg (154 lb) | 2,100 | 2.1 | 71.0 |
| 80 kg (176 lb) | 2,400 | 2.4 | 81.2 |
| 90 kg (198 lb) | 2,700 | 2.7 | 91.3 |
| 100 kg (220 lb) | 3,000 | 3.0 | 101.4 |
What counts and what does not
Your total water intake comes from drinks and from food. Fruit, vegetables, soup and many other foods are mostly water, and health guidance generally assumes that roughly a fifth of a person’s total water comes from what they eat. That is why this calculator estimates what you should drink rather than total water.
Water, tea, coffee, milk and juice all count for most people. Sugary drinks add calories, and alcohol makes you lose fluid, so water is a sensible default for the bulk of your intake.
Signs you are drinking enough, and too little
- Pale yellow urine, and passing it every few hours, usually means you are well hydrated.
- Dark yellow or amber urine, a dry mouth, headache, dizziness or feeling unusually tired can point to too little fluid.
- Thirst is a good guide for healthy people. Drink when you are thirsty, and do not wait for it to become strong.
- Older adults, and people who are ill, may feel thirst less, so a routine can help.
Can you drink too much?
Yes, though it is rare. Drinking a very large volume in a short time can dilute the sodium in your blood and make you seriously ill. It is most often reported in endurance events and in people forcing fluids beyond thirst. The sensible approach is to sip steadily through the day instead of drinking large amounts at once. People with kidney, heart or liver conditions, and anyone who has been told to limit fluids, should follow their doctor’s advice rather than this estimate.
Making it a habit
- Keep a bottle you like where you can see it, and use the bottle size in the plan to count refills.
- Tie drinking to things you already do, such as a glass on waking and one with each meal.
- Drink a bit more before and after exercise, and during it if it lasts more than about an hour.
- Cut back in the hour before bed if night-time trips to the toilet disturb your sleep.
Frequently asked questions
How much water should I drink a day?
There is no single number that fits everyone. Health agencies publish reference intakes for total water from drinks and food, for example about 2.0 litres a day for women and 2.5 litres for men in European guidance, and about 2.7 and 3.7 litres in United States guidance. About one fifth of that usually comes from food. This calculator gives a personal estimate of what to drink, based on your weight, exercise, climate and life stage.
How is my estimate worked out?
It starts with 30 ml of fluid for every kilogram of body weight, limited to a range of 1,500 to 3,500 ml. It then adds 10% in warm weather or 20% in hot weather, adds extra for exercise (about 6, 10 or 15 ml for each minute of light, moderate or vigorous activity), and adds 300 ml in pregnancy or 700 ml while breastfeeding. The result is rounded to the nearest 50 ml. It is a rule of thumb for healthy adults, not a medical measurement.
Is the 8 glasses a day rule true?
It is a handy round number, not a scientific law. Eight 250 ml glasses is 2 litres, which happens to be close to many adults' needs, but your own need can be well above or below that. Weight, heat, activity and diet all change it, and other drinks and food count too.
Do tea, coffee and other drinks count?
For most people, yes. Tea, coffee, milk, juice and soup all contribute to your fluid intake, and moderate amounts of caffeine for regular drinkers do not cancel that out. Water is still a good default because it has no sugar or calories. Alcohol is different, because it makes you pass more urine.
How do I know if I am drinking enough?
Thirst is a reliable guide for most healthy people, and the colour of your urine is a handy check. Pale yellow suggests you are well hydrated, while dark yellow or amber suggests you need more fluid. Headaches, dizziness, a dry mouth and unusual tiredness can also be signs of dehydration.
Can you drink too much water?
Yes, although it is uncommon. Drinking very large amounts in a short time, particularly during long endurance events, can dilute the sodium in the blood, a condition called hyponatraemia, which can be serious. Spread your drinks through the day and do not force fluids beyond thirst.
Should I drink more when I exercise?
Usually yes, because you lose fluid in sweat. The calculator adds an allowance for the minutes you exercise, but real sweat loss varies a lot between people and conditions. For long or intense sessions, weigh yourself before and after: each kilogram lost is roughly a litre of fluid to replace.
How much more do I need when pregnant or breastfeeding?
European guidance suggests about 300 ml extra a day in pregnancy and about 700 ml extra while breastfeeding, and the calculator applies those figures. Your own needs may differ, so follow the advice of your midwife or doctor.
Who should not use this estimate?
It is meant for healthy adults. Children and teenagers have different needs. If you have kidney disease, heart failure, liver disease, or take medicines such as diuretics, or if a doctor has told you to limit fluids, follow your doctor's advice instead of any online figure. If you feel unwell, get medical advice.
Is my information saved?
No. The calculation runs in your browser and nothing you enter is uploaded or stored on our servers.
Related calculators
For your daily calorie needs, use the TDEE calculator or the BMR calculator. To check your weight against your height, try the BMI calculator, and to estimate body composition, the body fat calculator.