How much water you need to drink a day
An online calculator for daily water intake. It works out the figure from EFSA guidance with adjustments for weight, physical activity and heat, and then shows the part that matters: how much of it arrives with food and other drinks and how much is left to drink as water. A glass tracker for today sits beside it.
How to use it
Adult, child, pregnancy or breastfeeding — then sex and weight. The result updates as you type.
Training and heat add volume for sweat losses.
The large figure is water itself. The bar below shows what the total is made of.
Tap a glass as you drink. Tomorrow the count starts again.
Find your daily figure and mark off what you have drunk
This much you actually need to drink
Drunk today
Tap a glass to mark it. The count is kept in this browser only and starts fresh tomorrow.
A better sign than any calculation is urine color: pale yellow means you are drinking enough.
Where "30 ml per kilogram" came from and why it is not a guideline
How to tell you are drinking enough — and when it is too much urine color · hyponatremia
Thirst is the main regulator, and in a healthy person it works well. The practical sign of drinking enough is pale yellow urine. Dark says have a drink; completely clear says you could have less.
More is not better. Drinking a great deal at once is more dangerous than drinking too little: the excess dilutes sodium in the blood, and that condition — hyponatremia — can be severe. So drink across the day rather than liters at a time. If a doctor has restricted your fluids, for heart or kidney disease, their figure outweighs any general guideline.
How this is calculated
The basis is the EFSA adequate intake: 2.0 L a day for women and 2.5 L for men, including water from food. Weight enters as an adjustment to that figure rather than as a formula of its own: a 90 kg person spends more than a 60 kg one, but not half as much again. Exertion and heat add volume for sweat losses. From the total, water from food (about 22%) and from other drinks (about 25%) is subtracted — what remains is what to drink as water. A glass counts as 250 ml.
Children, pregnancy and breastfeeding use their own EFSA figures rather than a correction to the adult one: below age nine the figure does not depend on sex, which is why the sex field is not shown there. The calculator is written for a healthy person — with heart or kidney disease your doctor’s figure outweighs any general guideline.
The addition covers sweat. A better guide than any formula: weigh yourself before and after — each kilogram lost is about a liter of fluid.
