Water Intake Calculator

Work out how much water to drink a day from EFSA and US National Academies reference intakes, in litres, ml, fl oz and glasses.

Reviewed by Dany, RightSums team · Updated

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health · Daily life · UK & US

Choose a reference, your sex and age band, and the calculator shows how much water you need a day from food and drink, and how much of that usually comes from drinks. The EFSA figures used in the UK and Europe are 2.0 litres for women and 2.5 litres for men, with 70% to 80% from drinks. The US National Academies figures are 2.7 and 3.7 litres, with about 80% from drinks. Pregnancy and breastfeeding raise both. Results appear in litres, millilitres, US fluid ounces, cups and glasses of your chosen size. Exercise and hot weather add guidance rather than a fixed amount. This is an estimate for healthy people, not medical advice.

Accepted inputs

  • Reference: EFSA (UK and Europe) or US National Academies
  • Sex, or prefer not to say
  • Age band (14 and over)
  • Pregnant or breastfeeding
  • Exercise minutes and hot weather
  • Glass or cup size in ml

Outputs

  • Water from drinks per day
  • Total water from food and drink
  • Litres, ml, US fl oz, US cups and glasses
  • NHS 6 to 8 glasses comparison
  • Exercise and heat tips

How to use the Water Intake Calculator

  1. Pick EFSA for the UK and Europe or the US National Academies, then choose your sex, or prefer not to say to see the range, and your age band.
  2. The calculator looks up the adequate intake of total water for that group and adds the published amount for pregnancy or breastfeeding if you select it.
  3. It then works out the share that usually comes from drinks, which is 70% to 80% under EFSA and about 80% under the US figures, since food provides the rest.
  4. Your result is shown in litres, millilitres, US fluid ounces, US cups and glasses of the size you enter, with tips if you exercise or it is hot.

Frequently asked questions

How much water should I drink a day?

EFSA suggests 2.0 litres of total water a day for women and 2.5 litres for men, from food and drink. With 70% to 80% from drinks, that is about 1.4 to 1.6 litres (47 to 54 fl oz) for women and 1.75 to 2.0 litres (59 to 68 fl oz) for men. The NHS says 6 to 8 glasses of fluid.

How many glasses of water a day is that?

With a 250 ml glass, a woman's 1.4 to 1.6 litres from drinks under EFSA is 5.6 to 6.4 glasses, and a man's 1.75 to 2.0 litres is 7 to 8 glasses. The NHS advises 6 to 8 glasses a day but gives no glass size; at 250 ml that is 1.5 to 2.0 litres. Tea, coffee and lower-fat milk count.

How much water should I drink a day in ounces?

The US National Academies set 2.7 litres (91 fl oz) of total water a day for women and 3.7 litres (125 fl oz) for men. About 80% comes from drinks, so that is roughly 73 fl oz, or 9.1 cups of 8 fl oz, for women and 100 fl oz, or 12.5 cups, for men. The rest comes from food.

How much water should I drink when pregnant or breastfeeding?

EFSA adds 300 ml a day in pregnancy, taking a woman to 2.3 litres of total water, and about 700 ml when breastfeeding, giving 2.7 litres. The US figures are 3.0 litres in pregnancy and 3.8 litres (128 fl oz) when breastfeeding, about 3.04 litres from drinks. Follow your midwife's or doctor's advice if it differs.

Do I need more water when I exercise or it is hot?

Yes, but the references give no fixed amount because sweat losses vary widely. The figures assume a mild climate and moderate activity. The American College of Sports Medicine suggests weighing yourself before and after exercise and avoiding a loss of more than 2% of body weight. Very active people in hot weather can need 6 litres or more a day.

Sources

The rates and rules in this tool come from:

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