Water Intake Calculator

Water makes up around 60% of your body and drives nearly every process in it — temperature control, circulation, digestion, and joint lubrication. This calculator estimates your daily fluid target from your body weight and activity level, and shows it in litres, cups, and fluid ounces.

How your target is estimated

The calculator uses a weight-based baseline plus adjustments for your activity, climate, and life stage:

• Baseline: about 35 ml per kg of body weight.
• Activity add-on: extra fluid to replace what you lose through sweat, from none when sedentary up to about a litre a day for hard training.
• Climate: add fluid in hot or humid conditions, where sweat and breathing losses climb.
• Pregnancy / breastfeeding: the Institute of Medicine sets higher adequate intakes — roughly +300 ml in pregnancy and +700 ml when breastfeeding.

For a 70 kg moderately active person in a temperate climate that’s roughly 2,450 ml baseline + 500 ml for activity ≈ 2.95 litres (about 100 fl oz, or 12–13 cups) per day.

What counts toward it

You don’t have to drink the whole amount as plain water:

• All fluids count — water, milk, tea, coffee, and juice all contribute.
• Food provides roughly 20% of your water, especially fruit and vegetables.

So the figure above is a total fluid target; a good chunk arrives through the food and drinks you already have.

Drink more when you need to

Your needs rise in heat and humidity, at altitude, during illness with fever or diarrhoea, and during pregnancy or breastfeeding. The best everyday guide is your body: aim for pale-straw-coloured urine and drink when you’re thirsty. Only in unusual endurance situations does drinking too much become a concern.