Does Coffee Count as Water? What the Studies Found

Coffee counts. A 12 oz (355 ml) mug adds 355 ml to your day, the same as a glass of water that size, as long as your caffeine stays in a sensible range.

This page covers the trials behind that answer, tea, and the caffeine ceiling. For every other drink, from milk to beer, see what counts toward your water intake.

Does Coffee Count as Water Intake?

Yes. When the US National Academies set the US water values, they found that caffeinated drinks can add to your daily water as much as drinks without caffeine. So a mug of coffee goes into your log at its full size, the same as water, tea or milk.

That holds for whatever daily number you aim for. Our main guide on how much water you should drink a day explains where those numbers come from.

Is Coffee Dehydrating?

Not at the amounts most people drink. In a 2014 trial, 50 men who drank coffee every day had four 200 ml (6.8 oz) mugs a day, and their body water matched their water-only days. Large doses of caffeine can make you pee more, but only for a short time.

What the 2014 Coffee Trial Measured

Each man went through two test periods in a random order: one with four mugs of black coffee a day, one with the same amount of water. The coffee carried 4 mg of caffeine per kg of body weight, which comes to about 280 mg for a 70 kg (154 lb) man.

The researchers tracked total body water with a tracer drink of heavy water (deuterium oxide), and checked blood, urine and body weight too. They concluded that moderate coffee "provides similar hydrating qualities to water" in men used to caffeine.

Is Coffee a Diuretic?

Mildly, at higher doses. The US National Academies report that caffeine above 180 mg a day can raise how much you pee, "perhaps transiently". That last word matters: the extra trips to the bathroom pass instead of lasting all day.

Keep in mind who the trials tested. The 2014 coffee drinkers already had 3 to 6 cups a day, so the result may not hold for someone who rarely drinks coffee and has a large one.

Does Tea Count as Water Intake?

Yes. In a 2011 trial, 21 men drank 4 or 6 mugs of black tea a day (240 ml, about 8 oz, each) or the same amount of water, and their blood and urine showed no difference. The NHS counts tea and coffee as fluid too, along with water and lower-fat milk.

Six of those mugs come to 1,440 ml (49 oz), more than half of a 2,500 ml (85 oz) daily goal. Hot tea and iced tea also matched water in the 2016 trial below.

Three Trials at a Glance

Each trial is small and tested men only. Taken together they point the same way, using three different designs.

How Much Caffeine Is Too Much?

For most healthy adults, the FDA names 400 mg a day as an amount not usually tied to harm. It puts that at about two to three 12 oz (355 ml) cups of coffee, or 710 to 1,065 ml (24 to 36 oz).

That ceiling matters more than the water question does.

Once your coffee passes two or three big mugs, switch the next drink to water or a caffeine-free one. The fluid counts the same, and the caffeine stops climbing.

How to Count Coffee in a Real Day

Maya weighs 65 kg (143 lb), walks to work and lives somewhere mild. Glubbo's habit formula gives her a goal of 1,900 ml (64 oz), and her day looks like this:

Your own goal will differ. The water intake calculator uses the same formula as the app: your weight, activity, climate and sex.

What About Lattes, Iced Coffee and Sweet Coffee Drinks?

They count, and so does the milk in them. The catch is sugar, which the NHS advises cutting by choosing sugar-free or no-added-sugar drinks.

• Filter coffee or americano: log the full mug.
• Latte or flat white: log the full cup, milk included.
• Espresso: log the shot, though it adds only a sip of fluid.
• Iced coffee: log the drink as you pour it.
• Syrup coffees and bottled sweet coffee: they count, but treat them like soda.

What to Do Today

Tonight, add up what you drank today with coffee and tea included, and compare it with your goal. If you only counted plain water before, the gap is probably smaller than you thought.

Food adds water on top of your drinks. The foods with the most water hold over 90 % water by weight, and a salad or a bowl of fruit can add a glass's worth to your day.