Skip to content
FitDiary

Water intake calculator: how much water should I drink a day?

See how much to drink each day based on your size, how active you are and the weather. It’s free, works in litres or fl oz and needs no sign-up.

Your details

Units
Sex
Height
How active are you?
Hot weather or sweating a lot?
Pregnant or breastfeeding?

Your result

Enter your age, height and weight to see how much water to drink.

How much water should you drink a day?

European and US guidelines put the water healthy adults need at 2 to 2.7 litres a day for women and 2.5 to 3.7 litres for men, counting food as well as drinks. About 80% comes from drinks, so drink roughly 1.6 to 2.2 litres a day if you’re a woman, or 2 to 3 litres if you’re a man.

You need more in hot weather, when you sweat a lot and when you’re pregnant or breastfeeding. The calculator above adjusts for all of these.

How the water intake calculator works

The calculator works out your total water in two ways and uses whichever is higher:

  1. The adequate intake for your sex from the European Food Safety Authority (EFSA): 2 litres a day for women and 2.5 litres for men, plus 300 ml in pregnancy and 700 ml when breastfeeding.
  2. 1 ml of water for every calorie you burn, a rule from the US National Research Council (1989). The calculator raises this to 1.5 ml per calorie for hot weather or heavy sweating, as the NRC allows. Your calories burned are your TDEE, calculated as on the TDEE calculator page, so a more active day means more water.
  3. Finally, it counts 80% of the total as the part to drink, because the US National Academies found that about 80% of total water comes from drinks and the rest from food. Results are rounded to the nearest 50 ml.

What the main guidelines say

SourceWomenMenWhat it counts
EFSA (2010)2 litres2.5 litresDrinks and food
US National Academies (2005)2.7 litres3.7 litresDrinks and food
NHS (UK)6 to 8 glasses6 to 8 glassesDrinks only

EFSA’s figures apply at moderate temperature and activity. The US figures are based on the typical intakes of healthy people, and the report says they aren’t a strict requirement. The NHS calls its 6 to 8 glasses “just a guide”.

You can log water in the FitDiary app and set your own daily target there. The app starts you at 2 litres.

Worked example

Take two people with ordinary routines:

  • A 30-year-old woman, 165 cm and 70 kg, lightly active, burns about 1,952 kcal a day. At 1 ml per calorie that’s under EFSA’s 2 litres, so her total is 2 litres and she should aim to drink about 1.6 litres (54 fl oz), or 6 glasses.
  • A 35-year-old man, 180 cm and 80 kg, moderately active, burns about 2,720 kcal a day. At 1 ml per calorie that’s above EFSA’s 2.5 litres, so his total is about 2.7 litres and he should aim to drink about 2.2 litres (74 fl oz), or 9 glasses.

On a hot day, at 1.5 ml per calorie, the woman’s total rises to about 2.95 litres and she should drink about 2.35 litres (79 fl oz).

How much water should I drink per day: chart

How much to drink each day, by the calories you burn. Not sure how many that is? The TDEE calculator tells you.

Calories burned a dayWomenMenHot weather or heavy sweating (women and men)
1,800 kcal1.6 L (54 fl oz)2 L (68 fl oz)2.15 L (73 fl oz)
2,000 kcal1.6 L (54 fl oz)2 L (68 fl oz)2.4 L (81 fl oz)
2,200 kcal1.75 L (59 fl oz)2 L (68 fl oz)2.65 L (90 fl oz)
2,500 kcal2 L (68 fl oz)2 L (68 fl oz)3 L (101 fl oz)
2,800 kcal2.25 L (76 fl oz)2.25 L (76 fl oz)3.35 L (113 fl oz)
3,200 kcal2.55 L (86 fl oz)2.55 L (86 fl oz)3.85 L (130 fl oz)

Drinks only, rounded to the nearest 50 ml. Pregnancy adds about 250 ml of drinks a day and breastfeeding about 550 ml (80% of EFSA’s 300 and 700 ml).

Glasses of water in ml and fl oz

Glasses250 ml glasses8 fl oz glasses
6 glasses1.5 L (51 fl oz)48 fl oz (1.4 L)
8 glasses2 L (68 fl oz)64 fl oz (1.9 L)
10 glasses2.5 L (85 fl oz)80 fl oz (2.4 L)
12 glasses3 L (101 fl oz)96 fl oz (2.8 L)

A glass in the UK is often 200 to 250 ml; in the US a glass is usually counted as 8 fl oz (about 237 ml).

Does coffee count towards your water intake?

Yes. The NHS says water, lower-fat milk and lower-sugar drinks, including tea and coffee, all count. The US National Academies came to the same view: caffeine can make you pass more urine for a short time, but caffeinated drinks still add to your daily water.

Food counts too. Soup, fruit, vegetables, yoghurt and cooked grains are mostly water, which is why the calculator leaves about a fifth of your total to food.

Sugary drinks and juice count as well, but they add calories.

When you need more water

  • In hot weather or a hot workplace, and whenever you sweat a lot. Choose ‘Yes’ for hot weather in the calculator.
  • During long or hard exercise. The NHS advises drinking extra fluids to replace what you lose through sweat.
  • In pregnancy (about 300 ml more a day in total) and while breastfeeding (about 700 ml more), according to EFSA.
  • When you’re ill with a fever, vomiting or diarrhoea. Ask a pharmacist or doctor what to drink.

This calculator is for healthy adults. If you have kidney, heart or liver problems, or a doctor has told you to limit fluids, follow their advice instead.

Log your water and your lunch in one sentence

Type ‘chicken wrap and 500 ml of water’ and FitDiary logs the meal and the water together. Set your own daily water target in the app.

Download on the App StoreGet it on Google Play

See how the FitDiary calorie counter works.

Frequently asked questions

How do I calculate how much water I should drink every day?

Start from the EFSA adequate intake for your sex (2 litres a day in total for women, 2.5 for men) or 1 ml for every calorie you burn, whichever is higher. Use 1.5 ml per calorie in hot weather. About 80% of that total is what you need to drink.

How much water should I drink a day according to the NHS?

The NHS suggests 6 to 8 cups or glasses of fluid a day, and calls it a guide. Water, lower-fat milk and lower-sugar drinks, including tea and coffee, all count. You may need more in hot weather or after sweating from exercise.

Does coffee count towards water intake?

Yes. Tea and coffee count towards your daily fluid, according to both the NHS and the US National Academies. Caffeine can make you pass more urine for a short while, but the drink still adds to your daily water.

How many ounces of water are in 10 glasses?

With 8 fl oz glasses, 10 glasses are 80 fl oz, about 2.4 litres. With 250 ml glasses, 10 glasses are 2.5 litres, about 85 fl oz.

How much water should a woman drink a day?

EFSA puts the total for women at 2 litres a day and the US National Academies at 2.7 litres, counting food. From drinks, that’s roughly 1.6 to 2.2 litres. Pregnancy adds about 300 ml and breastfeeding about 700 ml to the total.

Can you drink too much water?

Yes, although it’s rare in healthy adults. Drinking several litres in a short time, more than your kidneys can clear, can lower the salt level in your blood. Spread your drinks through the day and let thirst guide you.

How do you know if you’re drinking enough water?

Pale yellow urine and rarely feeling thirsty are good signs. Dark yellow urine, peeing less often and feeling thirsty most of the day can mean you need to drink more.

Related calculators