Water Intake Calculator

Enter your weight, how much you exercise and the weather to get a general estimate of how much to drink in a day, shown in litres and glasses. Everything runs in your browser.

Body weight

Exercise per day: 30 minutes

Estimated drinks per day

2.6 L

That is about 2,560 ml, or 10 glasses of 250 ml (about 8 oz). A reasonable range is 2.3 to 2.8 L.

Base need: 2.3 L
Exercise: +0.3 L
Heat: none
Per waking hour: 160 ml

For comparison, the US National Academies suggest about 2.7 L of total water a day for women, which includes the roughly 20% that comes from food. Other drinks such as tea, milk and juice count too.

Needs change with health, medicines, pregnancy, breastfeeding, age and illness. Drinking far more than you need can also be harmful, so follow your doctor's advice, and thirst and pale yellow urine are useful everyday guides.

How the estimate is worked out

A widely used starting point is about 33 ml of fluid per kilogram of body weight each day. The calculator adds 0.5 L for every hour of exercise and 0.5 L for hot or humid weather. The range shown is 10% either side, because needs vary from person to person and day to day.

Daily water by body weight

Base need at 33 ml per kg, before exercise and weather. A glass here is 250 ml.

Weight	Litres a day	Glasses (250 ml)
50 kg (110 lb)	1.65 L	6.6
60 kg (132 lb)	1.98 L	7.9
70 kg (154 lb)	2.31 L	9.2
80 kg (176 lb)	2.64 L	10.6
90 kg (198 lb)	2.97 L	11.9
100 kg (220 lb)	3.30 L	13.2

What counts toward your water

Water, tea, coffee, milk, juice and other drinks all count.
About 20% of your daily water comes from food, especially fruit and vegetables.
The US National Academies suggest about 2.7 L (women) and 3.7 L (men) of total water a day, including food.

When you may need more or less

More: hot weather, exercise, fever, vomiting or diarrhoea, pregnancy and breastfeeding.
Different: kidney, heart or liver disease and some medicines. Your doctor may give you a specific limit.
Too much is also risky. Very large amounts in a short time can dilute the sodium in your blood, which can be dangerous.

Easy signs you are drinking enough

Pale yellow urine.
You rarely feel thirsty.
Spreading drinks through the day instead of all at once.

How to use the Water Intake Calculator tool

Choose your units and type your body weight.
Move the slider to the minutes of exercise you do on a typical day.
Say whether the weather is mild or hot and humid.
Read the daily estimate in litres, millilitres and glasses, and the range around it.

Frequently asked questions

How much water should I drink a day?

A common starting point is about 33 ml per kg of body weight, so about 2.3 L for a 70 kg person, plus extra for exercise and heat. The US National Academies suggest about 2.7 L (women) and 3.7 L (men) of total water a day including food.

Does tea, coffee or food count?

Yes. About 20% of daily water comes from food, and drinks such as tea, coffee, milk and juice count toward your fluids. Water is still the best everyday choice.

How much extra water do I need when I exercise?

About 0.35 to 0.6 L more for each hour of exercise is a common guide, and more in the heat. This calculator adds 0.5 L per hour of exercise and 0.5 L for hot weather.

Can I drink too much water?

Yes. Drinking a very large amount in a short time can dilute the salt in your blood, which is dangerous. Spread your drinks through the day, drink to thirst, and follow your doctor's advice if you have a condition such as kidney or heart disease.

How can I tell if I am drinking enough?

Pale yellow urine and rarely feeling thirsty are good signs. Dark urine, headaches, dizziness or a dry mouth can mean you need more fluid.