Water intake calculator

How much water should I drink a day?

The NHS Eatwell Guide recommends 6 to 8 cups or glasses of fluid a day. Water, lower-fat milk and sugar-free drinks, including tea and coffee, all count. With a standard 250ml glass that's 1.5 to 2 litres.

The European Food Safety Authority (EFSA) gives a more detailed figure. Its adequate intake of total water for adults is 2.0 litres a day for women and 2.5 litres a day for men. That total includes the water in your food, which usually provides about 20% to 30% of it. Fruit, vegetables, soup, yoghurt and even bread all contain water.

How the water intake calculator works

The calculator starts from the EFSA total and assumes 20% comes from food, the low end of the range, so the amount it suggests from drinks is on the generous side:

drinks = EFSA total water × 0.8
+ exercise minutes ÷ 60 × 0.4 to 0.8 litres

The EFSA figures assume a moderate climate and moderate activity. For exercise, the calculator adds 0.4 to 0.8 litres an hour, the starting range the American College of Sports Medicine suggests for exercise. It uses 0.4 litres an hour in cool or mild weather, 0.6 when it's warm and 0.8 when it's hot, because you sweat more in the heat. Your own sweat rate could be lower or higher than this.

Worked examples

• A woman with no exercise: 2.0 litres total × 0.8 = 1.6 litres from drinks, about six or seven 250ml glasses.
• A woman doing a 30-minute run on a mild day: 1.6 + (30 ÷ 60 × 0.4) = 1.6 + 0.2 = 1.8 litres, about seven glasses.
• A man with no exercise: 2.5 × 0.8 = 2.0 litres, eight 250ml glasses.
• A man playing football for an hour on a hot day: 2.0 + 0.8 = 2.8 litres, about 11 glasses.

Daily fluid at a glance

What counts towards your fluid intake?

• Water is the best choice: it has no calories and is good for your teeth.
• Tea and coffee count. Caffeine has a mild effect, but these drinks still hydrate you overall.
• Lower-fat milk counts and adds calcium and protein.
• Fruit juice and smoothies count, but the NHS suggests no more than 150ml a day in total because they're high in sugar.
• Alcohol doesn't help. Use the alcohol units calculator to keep an eye on how much you drink.

Signs you need to drink more

Feeling thirsty, dark yellow or strong-smelling pee, peeing less often than usual, feeling dizzy or tired, a dry mouth and headaches can all be signs of dehydration. The simplest check is the colour of your pee: aim for a pale straw colour. You'll need more fluid in hot weather, when you're active, if you have a high temperature, or if you've had diarrhoea or been sick.

Older people, babies and young children are more at risk of becoming dehydrated, so keep drinks within easy reach for them.

Practical tips

• Have a drink with every meal and keep a refillable bottle with you.
• On a training day, drink before you go and sip during longer sessions. The running pace calculator can help you see how long your run will take.
• You don't need to force down huge amounts. Drinking far more than your body needs doesn't add any benefit, and drinking very large volumes in a short time can be harmful.

Some people are told to limit their fluid, for example with heart failure or kidney disease. If that's you, or you're pregnant or breastfeeding, follow the advice of your doctor or midwife rather than this calculator. If you're always thirsty or peeing a lot, speak to your GP, as it can be a sign of a condition such as diabetes.

Last reviewed October 2026 using 2026/27 figures. This calculator gives an estimate for guidance only.