Water intake calculator

How this water calculator works

There is no exact science to daily water needs, so this uses the most common working rule: about 35 ml per kilogram of bodyweight as a baseline, then adds roughly 600 ml per hour of exercise, more for a physical job, and more again on a hot day. The NHS advice of "6 to 8 glasses" lands around 1.5–2 litres, which is what this gives for an average-sized person on a normal day - the calculator just adjusts it for size, work and training.

Does it have to be water?

No. Tea, coffee, milk, squash and sugar-free drinks all count. Alcohol does not. Around a fifth of your fluid comes from food, especially fruit, veg, soup and yoghurt, which is why the note above suggests slightly less than the total as drinks.

Why it matters for training and fat loss

Even mild dehydration knocks strength and endurance and makes a session feel harder than it is. It also gets mistaken for hunger. If you are dieting and find yourself snacking in the afternoon, a pint of water first is a cheap experiment.

Can you drink too much?

Yes, though it is rare - forcing several litres in a short time can be dangerous. Spread it out, drink to thirst during long sessions, and if you are training hard for over an hour in heat, an electrolyte drink or a pinch of salt in your food helps you hold on to it.

FAQs

How much water should I drink a day in the UK?

The NHS suggests 6 to 8 glasses (about 1.5 to 2 litres) a day for most adults. Bigger people, physical jobs, training and hot weather push that up. A quick rule is 35 ml per kilogram of bodyweight, plus extra for exercise.

How much water should I drink when working out?

Roughly 500 to 750 ml per hour of exercise on top of your normal intake, more in the heat. Drink to thirst during the session and top up afterwards.

Does coffee count towards water intake?

Yes. The caffeine in normal amounts of tea and coffee does not cancel out the fluid. Alcohol is the exception - it dehydrates you.

Does drinking water help you lose weight?

Not directly, but it helps. Thirst is often mistaken for hunger, a glass before meals makes it easier to eat less, and swapping sugary drinks for water removes calories without you noticing.