How Many Ounces Are In a Half-Gallon of Water?

Globally, the average person drinks 8 cups or 1/2 gallon per day, which can be below one’s required individual water consumption to stay well-hydrated, based on one’s body weight and age. In the United States, based on 2015 to 2018 data, children and adolescents drank an average of only 23 ounces (0.18 U.S. liquid gallons) of plain water daily, and adults drank an average of 44 ounces (0.34 U.S. liquid gallons) of plain water daily.

Yet, water is a vital nutrient for every living cell. It acts as a building material for our bodies, forms our saliva, lubricates our joints, boosts skin health and beauty, regulates our internal body temperature, metabolizes and transports food in the bloodstream, flushes waste from the body, and acts as a shock absorber for the brain, spinal cord, and fetus.

How many bottles of water should you drink?

Health experts generally recommend 8 x 8-ounce glasses equivalent to 2 liters or half a gallon of water every day. However, you must make sure that you drink the required amount of water for your weight. Many people assume that 8 glasses of water is enough to hydrate themselves, but this can be misleading if your weight requires more. As body weight increases, fluid needs also increase.

Your body’s specific water requirements would also depend on your birth sex, health, life stage, diet quality, the intensity of daily activities, and the climate of the environment you’re in.

Birth sex

According to the Mayo Clinic, the U.S. National Academies of Sciences, Engineering, and Medicine recommend the following daily water intake:

  • For adult males, 15.5 cups or 3.7 liters
  • For adult females, 11.5 cups or 2.7 liters

Males need more fluids intake to support lower average body fat, increased body mass, and increased daily calorie burn.

Fluids intake would include not just water but also fluids from other beverages and food, However, it is recommended to drink plain water more as it is calorie-free, caffeine-free, and alcohol-free.


If you’re constipated or have a fever, or are generally feeling unwell, it is best to drink even more water than your required minimum daily intake. Water not only keeps you hydrated but helps flush out toxins from the body, as it regulates your internal body temperature.

You also need more water intake to replace fluids lost to congestion, fever, diarrhea, vomiting, and other similar factors. If you’re taking medicines, some medicines can contribute to dehydration.

If you become dehydrated, you will feel more unwell, experience lightheadedness or dizziness, headaches, decrease in urination and storing up more toxins in your body, dry mouth and mucous membranes (nostrils, lips, gums), decreased skin elasticity, low blood pressure, kidney problems, and even death with severe dehydration.

As a general rule, on average, a person can go without food for up to two months as long as there is enough water intake. But, without water intake, a person can only survive for 3 days.

Life stage

Older, more active children need water. People with more fatty tissue need more water than those with less fatty tissue. So do pregnant women, as they require additional fluids to maintain adequate amniotic fluid levels to ensure the baby’s healthy and steady growth. Older seniors require additional fluids, too, as not only does the amount of water but also the sensation of thirst decreases with age. This can lead to undetected dehydration.

Diet quality

If you eat a lot of fresh fruits and vegetables, which are packed with water (except for parsley and asparagus), you won’t need to drink as much water as a person who eats food with a lot of sodium. The top dehydrating foods are salty food, protein from meats, parsley, and asparagus (which are diuretics), soy sauce, sugary treats, fast food and fried food, and alcohol.

Daily activities

When you perspire a lot due to exercise or strenuous physical activities, you need more water to replace the fluids you’ve lost throughout the day. The duration and intensity of the physical activity you engage in also affect how much you sweat and your body’s fluid needs. However, people perspire at different rates and it’s difficult to calculate exact hydration losses and fluid intake needs based on their activity level alone. Generally, the more physical exertion you engage in, the more water you should drink.


According to a Sports Medicine study, genetics and how accustomed your body is to a given climate affect perspiration volume. You would also need to drink more water on hot summer days than in winter. However, the dry air from high-altitude, cold climates can also cause fluid loss. Due to frigid temperatures, our bodies can also burn a lot of carbohydrates which leads to fluid loss.

Thirst is usually the first sign of mild dehydration, so go by your thirst. If you’re feeling thirsty wherever you are, drink more water promptly.

How to Calculate the Amount of Water You Need to Drink Daily

To calculate how much water you should drink based on your weight, experts recommend this formula:

  1. Take your weight in pounds and divide it by 2.2. If you’re taking it in kilograms, it should be as it is, since 1 kilogram is equal to 2.2 pounds.
  2. If you’re younger than 30, multiply the weight by 40. If you’re between 30 to 55 years old, multiply it by 35. If you’re older than 55, multiply it by 30.
  3. Divide the product by 28.3.
  4. The quotient is the number of ounces of water you should drink each day.

So, for example, if someone named Stan is 33 years old and weighs 150 pounds —

  1. Divide 150 by 2.2 to get his weight in kilograms (68.18 kilograms).
  2. Since he’s between 30 to 55 years old, multiply 68 by 35.
  3. This results in 2,386.36,
  4. Which is then divided by 28.3. The final result is 84.32 ounces, which is the amount of water Stan should drink each day.

This gets tricky if you’re a gallon person and you want to find out how many ounces are in a gallon, or you’re an ounce or cup person and how many ounces or cups you will need to drink at least half a gallon of water daily if you go by the general rule-of-thumb. Do you mean a liquid ounce or a dry ounce? Do you mean the U.S. gallon or the U.K. imperial gallon? How much are 84.32 ounces of water in cups or glasses or gallons?

These next sections will run you through the basics of ounce conversion.

What is an ounce?

An ounce is a unit measure of volume. It can refer to dry ounce or fluid ounce. A dry ounce measures dry matter, like the amount of cocoa powder you use in baking chocolate cake. Dry ounces are measured on a scale. Fluid ounce refers to liquid matter, like the amount of water you use in baking that chocolate cake. Fluid ounces are measured through a measuring cup.

Why is fluid ounce expressed as “oz”?

“Ounce” comes from the Latin word “uncia”, meaning “one-twelfth” of a Roman foot. “Uncia” is also the same root word for “inch”, A physical standard was the copper bar, which was divided into 12 equal parts known as “unciae”.

“Uncia” is where the Italian word “onza” (meaning “ounce”) comes from. It was loosely used in the 14th century, to indicate “a small quantity”. In Middle English, it was also used as a measure of time (7.5 seconds) and length (around 3 inches). “Oz” is the shortened version of “onza”.

What are the U.K. and U.S. Weighing Systems?

The U.K. and U.S. weighing systems evolved from the different medieval systems of weights and measures. Although the International System of Units (SI) is the most commonly used international standard of measurement today, the U.K. and U.S. weighing systems persist in use,

The only difference between the U.K. and U.S. weighing systems is in volume measurements. The number of ounces in pints, quarts, and gallons are all larger in the U. K. or imperial system, but the size of the fluid ounce is larger in the U.S. system. The U.K. or imperial fluid ounce is equivalent to 28.41 mL in the metric system, while the U.S. fluid ounce is equivalent to 29.57 mL.

Officially, only 3 countries in the world still use the imperial system of measurement — the United States, Liberia, and Myanmar. The United Kingdom, where the imperial system originated, uses both the imperial and metric systems. Other countries which were former Commonwealth countries, like Australia, Canada, India, and South Africa, also use both the imperial and metric systems.

In both the U.K. and the U.S. weighing systems for fluid, the smallest unit is the fluid oz., then the pint, the quart, and the liquid gallon. In the U.K. system, the gill is also used, which comes after the fluid oz., but it is not commonly used in the U.S. The cup is not as commonly used in the U.K. system but is the unit of measure that comes after the fluid the U.S.

So, in the U.K. system, the following are the volume measurement equivalencies —

1 fluid oz. = 28.41 mL

1 gill = 5 fluid oz. (142.07 mL)

1 pint = 2o fluid oz. (568.26 mL)

1 quart = 40 fluid oz. (1.137 L)

1 gallon = 160 fluid oz. (4.546 L)

In the U.S. system —

1 fluid oz. = 29.57 mL

1 cup = 8 fluid oz. (236.59 mL)

1 pint = 16 fluid oz. (473.18 mL)

1 quart = 32 fluid oz. (946.36 mL)

1 gallon – 128 fluid oz. (3.785 L)

How many ounces are in a half-gallon of water?

In the U.K. imperial system, it’s 80 fluid oz., while in the U.S. system, it’s 64 fluid oz.

How much is 64 oz. of water?

In the U.K. imperial system, 64 fluid oz. of water is 1818.24 mL (28.41 mL/fluid oz. multiplied by 64), or 0.40 imperial gallons of water. In the U.S. system, 64 fluid oz. is 1,892.48 mL (29.57 mL/fluid oz. multiplied by 64), or half a gallon of water.

How much are 2 liters of water?

In the U.K. imperial system, 2 liters of water is equivalent to 3.5196 pints, or almost half a gallon (there are 8 pints in an imperial gallon). In the U.S. system, 2 liters is equivalent to 4.226 fluid pints, or also almost half a gallon (there are 9.6076 fluid pints in a U.S. gallon).

How many ounces are 2.7 liters?

In the U.K. imperial system, 2.7 liters of water is 95.037 fluid oz or around 60% of an imperial gallon. In the U.S. system, it’s equivalent to 91.298 fluid oz., or around 71% of a U.S. gallon.

How much is a glass of water?

A standard glass of water is around 8 fluid oz. or around 240 mL, in the U.S. system. It is commonly expressed in cups in the U.K. system, which is around 10 imperial fluid oz. or around 250 mL of water.

To address our previous hypothetical case of Stan who needs to how much 84.32 ounces is in cups, glasses, or gallons of water he must drink daily based on his age and weight —

In the U.K. system, 84.32 imperial ounces is around 10 imperial cups or 0.63 gallons (2.86 liters). In the U.S. system, 84.32 ounces is 10.5 U.S. cups, or 16.8 U.S. glasses, or 0.66 U.S. gallons (3 liters).

Stan would need to drink more water using the U.S. system than if he’s using the U.K. imperial system.

How to Drink More Water Daily

The top 3 recommended and no- to least-expense practices for drinking more water daily are:

(1) Drink as soon as you wake up.

Most of us go to the bathroom to relieve ourselves as soon as we wake up. Why not make it a habit to drink water, too, as soon as you wake up? You can do this by placing a pre-filled 16-oz. water bottle on your bedstand as an automatic reminder or going to the water dispenser or refrigerator for your two 8-ounce glasses of water right after your bathroom trip. This way, you get a headstart on your day with at least one-fourth of your daily water intake need already fulfilled.

Aside from this, drinking water as soon as you wake up has several health and beauty benefits: it jumpstarts your metabolism, strengthens your immune system, helps weight loss, increases skin radiance for a more flawless complexion, increases hair shine and texture, relieves heartburn and indigestion, helps weight loss, improves your digestive system, and inhibits kidney stones and bladder infections. For boosting metabolism and promoting digestion, room temperature or warm water is recommended instead of cold water.

(2) Eat more fresh produce.

Instead of snacking on junk food, develop the habit of snacking on water-packed fruits or leafy green salads instead. Munching on an apple can provide you with the equivalent of half a glass or cup of water. Add extra tomatoes to your salad, and get generous servings of berries, citrus, melon, grapes, and other fruits.

(3) Bring a bottle everywhere.

Keep a bottle in your bag, in your car, or within view wherever you spend most of your time. This provides you with a natural visual cue to drink water first instead of reaching out for other snacks. Making a habit of drinking water first at least 30 minutes before taking in food not only reduces cravings but also helps your digestion.

But Don’t Drink Too Much Water, Either!

As you transition into the habit of more water drinking, it’s also important not to do it with too much, too soon, flooding your system all at once. This can cause hyponatremia or water intoxication. It is a condition where the electrolytes in your body are depleted because the body’s sodium levels are quickly diluted. When the sodium level drops too quickly, fluids move out of the bloodstream and into tissue cells, causing tissues to expand or swell.

Common symptoms of hyponatremia are headaches, nausea or vomiting, bloating, muscle spasms and cramping, swollen hands and feet, restlessness and irritability, tiredness, and altered mental states.

Do it gradually instead, as long as you feel well drinking more water.

Read More: How Much Does A Brick Weigh?

How Do I Know If I’m Drinking Enough Water?

Aside from frequent urination, you’ll know you’re drinking enough water when your urine is a clear or pale yellow, less odorous, and you have daily soft bowel movements. Once you’ve made it into a habit, you’ll also notice your skin becoming smoother, even glowing, as your hair takes on a richer and shinier texture. Your joints work better, your mind is sharper, you could lose excess weight, and your heart works better. Of course, overall, you’ll also feel a lot better and healthier.

Drinking the minimum amount of water daily based on one’s age and weight is highly recommended for healthier living. One must also consider the contexts of one’s birth sex, health, life stage, diet quality, activity level and intensity, and environmental climate in adjusting for one’s minimum daily water intake. One must also consider whether they will use the U.K., the U.S., or the international standard metric system in water measurements. Whichever one chooses, the important thing is to use it consistently.

Drinking water has no adverse health side effects, except if one drinks too much, which can result in water intoxication. As long as one is drinking enough water and feeling well about it, the health and beauty benefits one enjoys are worth it.

Nick Spieth

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