Water Intake Calculator

For many women, roughly yes. For most men it is low: the reference figure is about 100 oz of drinks a day, against 73 oz for women.

The eight-glasses rule is easy to remember and was never based on evidence. Treat it as a floor rather than a target, and adjust for your size and activity.

A common starting point is half your body weight in ounces. For a 135 lb person that is about 68 oz, and for a 200 lb person about 100 oz.

Then add roughly 12 oz per 30 minutes of exercise, and more in hot or humid weather.

Yes. All drinks contribute to your total, and moderate caffeine does not dehydrate you despite how often that is repeated.

Caffeine has a mild diuretic effect, but the water in the cup more than covers it. Food adds roughly another 20% on top of what you drink.

Urine colour is the simplest check. Pale straw is about right; consistently dark yellow suggests you need more, and completely clear may mean you are overdoing it.

Thirst is a reasonable guide for healthy adults too, though it becomes less reliable with age, which is one reason older adults are more prone to dehydration.

Yes, though it is rare. Drinking very large amounts quickly can dilute blood sodium, a condition called hyponatremia, which is dangerous.

It usually happens in endurance events where people drink heavily while losing salt through sweat. Spreading intake through the day rather than forcing large volumes at once avoids it entirely.

The requirement changes little, but the thirst signal weakens with age, so older adults often drink less than they need without noticing.

Some medications, particularly diuretics, also increase losses. Drinking to a schedule rather than waiting for thirst is often advised for older adults.