Water Intake Calculator
How much water should you drink a day? Enter your weight, how much you exercise and the weather where you live to get a personal daily target in litres, glasses and ounces, plus a simple plan to spread it through the day.
A simple drinking plan
Important: if you have kidney disease, heart failure or liver disease, your doctor may limit how much you drink, so follow their advice instead. Do not drink more than about 1 litre an hour, even in hot weather.
How much water should you drink a day?
Most healthy adults need roughly 2 to 2.5 litres of fluid a day from drinks, and more in hot weather or when active. The European Food Safety Authority (EFSA) sets total water intake, from both drinks and food, at 2.0 litres a day for women and 2.5 litres for men. About 20% of that usually comes from food, such as fruit, vegetables, dal, rice and curries.
| Group | Total water per day (drinks + food) | From drinks (about 80%) |
|---|---|---|
| Women | 2.0 litres | about 1.6 litres (6–7 glasses) |
| Men | 2.5 litres | about 2.0 litres (8 glasses) |
| Pregnant women | 2.3 litres | about 1.8 litres |
| Breastfeeding women | 2.7 litres | about 2.2 litres |
These are baseline amounts for mild weather and light activity. A personal target based on body weight is often more useful, especially for larger or very active people.
How this calculator works
It starts with 33 ml of fluid per kg of body weight (about 0.5 oz per pound), with a sensible minimum based on the EFSA values for your sex. Body weight above 100 kg is not counted, because extra body fat does not need much extra water. Then it adds:
| Factor | Extra fluid |
|---|---|
| Exercise | 350 ml for every 30 minutes (about 0.7 litres an hour) |
| Hot or humid weather | 500 ml |
| Very hot weather or outdoor work | 1,000 ml |
| Pregnancy | 300 ml |
| Breastfeeding | 700 ml |
Example: a 70 kg man who exercises for 30 minutes in hot weather needs 70 × 33 = 2.31 litres, plus 0.35 litres for exercise and 0.5 litres for the heat, which is about 3.2 litres a day, or 13 glasses.
Is 8 glasses of water a day right?
The "8 glasses a day" rule (about 2 litres) is a reasonable rough guide for many adults, but it is not based on strong science. Smaller, less active people in cool weather may need less, while larger people, athletes and anyone in hot weather usually need more.
Does tea, coffee and food count?
Yes. Tea, coffee, milk, lassi and soups all count towards your fluid intake. Caffeine has only a mild effect on urine output in regular drinkers. Water is still the best everyday choice because it has no sugar or calories; sugary drinks and juice add a lot of sugar (see the Sugar Intake Calculator). Watery foods like watermelon, cucumber, oranges, yogurt and soups also help.
How to tell if you are drinking enough
| Urine colour | What it usually means |
|---|---|
| Pale straw or light yellow | Well hydrated |
| Dark yellow | Drink more water |
| Amber or honey-coloured | Dehydrated; drink water now |
| Completely clear, all the time | You may be drinking more than you need |
Other signs of dehydration include thirst, a dry mouth, headache, tiredness, dizziness and passing urine less often. Some vitamins and medicines can change urine colour.
Can you drink too much water?
Yes, although it is rare. Drinking very large amounts quickly can dilute the sodium in your blood (hyponatremia), which can cause nausea, headache, confusion and, in severe cases, seizures. Healthy kidneys can clear about 0.8 to 1 litre an hour, so spread your drinking through the day. During long endurance events, drink to thirst and use electrolyte drinks rather than only plain water.
Staying hydrated in hot weather and Ramadan
In very hot summers, drink regularly before you feel thirsty, carry a bottle and take ORS or a pinch of salt with lemon water if you sweat heavily. During Ramadan, spread your fluid between iftar and suhoor, for example 2 glasses at iftar, 4 to 6 glasses through the evening and 2 glasses at suhoor, and limit salty and fried foods, which increase thirst.
Frequently asked questions
How much water should I drink based on my weight?
A common guide is about 30–35 ml per kg of body weight, or about half an ounce per pound. For a 60 kg person, that is roughly 2 litres a day, plus extra for exercise and heat.
How many litres of water a day for a woman?
Around 1.6 to 2 litres from drinks for most women in mild weather, more when active, pregnant, breastfeeding or in hot weather.
How much water should I drink when exercising?
Around 400–800 ml per hour of exercise is typical, depending on how much you sweat. Drinking a glass before you start and sipping during exercise works well for most people.
Is drinking 4 litres of water a day too much?
For a large, active person in hot weather, it can be appropriate. For a small, inactive person it is more than needed, but usually harmless if spread through the day. Avoid drinking more than about 1 litre an hour.
Does drinking water help with weight loss?
Drinking a glass of water before meals can help you feel fuller, and swapping sugary drinks for water cuts calories. Use the Calorie Calculator to plan your intake.