Written by Hrefna Palsdottir, ms — median reviewed by Kim Chin, RD, Nutrition — updated on October 12, 2021

You’ve most likely heard the you should drink eight 8-ounce (240-ml) glasses that water each day. That’s half a gallon that water (about 2 liters).

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This case has become widely accepted as fact, and it’s very easy come remember. However is there fact to this advice, or is it simply a myth?

This article reviews the proof behind the “eight glasses a day” rule and how much water we need each day.

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It’s hard to pinpoint specifically where and also when the “eight glasses per day” dominion originated. There are theories that it might be based on a fluid intake that 1 ml every calorie of food consumed.

For someone eating a diet that 2,000 calories per day, this adds as much as 2,000 ml (roughly 64 ounces), or eight 8-ounce glasses.

However, a cultivation body of research suggests that this large recommendation might actually be too lot water for part people and also not enough for others.

While over there are absolutely circumstances in which water needs increase, healthy human being generally don’t should be spend water in such big quantities.

On the other hand, not drinking enough water can cause mild dehydration, defined as the loss of 1–2% of human body weight because of fluid loss. In this state, you might experience fatigue, headache, and also impaired mood (1).

But in bespeak to stay hydrated and avoid gentle dehydration, friend don’t should rigorously follow the eight glasses rule — merely follow her thirst.


There is no scientific evidence to support the 8×8 rule. Water requirements vary through individual, and also you have to let thirst guide your intake.

it’s not just plain water that supplies your body with water. Other beverages, prefer milk and also fruit juice, count together well.

Contrary to famous belief, caffeinated beverages and also mild alcoholic drink such together beer may additionally contribute to fluid intake, at the very least when they’re consumed in moderation (2, 3, 4).

Many the the foodstuffs you eat also contain significant amounts that water.

How lot water you gain from food depends on the lot of water-rich foods items you eat. Fruits and vegetables are specifically rich in water, and foods like meat, fish, and eggs likewise have a relatively high water content.

For example, watermelon is 91% water, and eggs room 76% water (5, 6).

Lastly, little amounts that water are developed within your body once you metabolize nutrients. This is referred to as metabolic water (7).

People that don’t gain much water from foodstuffs need come drink much more than those that eat much more water-rich foods.


Besides water, various other foods and also beverages girlfriend ingest also contribute to your as whole daily input of fluids and aid keep girlfriend hydrated. Some water is likewise created within her body v metabolism.

While this may certainly be used as a guideline, there room a variety of factors, both inside your body and in her environment, that affect your need for water.

Body size, composition, and task level vary considerably from human being to person. If she an athlete, live in a hot climate, or are currently breastfeeding, your water requirements increase (16).

Taking all this right into account, that clear that water demands are very individual.

Eight glasses the water per day might be much more than sufficient for part people, but it may be too small for others.

If you want to save things simple, simply listen to her body and let thirst be her guide. Drink water once you’re feeling thirsty. Stop when you’re not thirsty anymore. Comprise for liquid loss through drinking much more during hot weather and also exercise.

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However, keep in mind the this go not apply to everyone. Some older adults, for example, might need to consciously remind themselves come drink water, due to the fact that aging can reduce the sensation of thirsty (17).