How Much Does a Gallon of Milk Weigh?

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So, you’ve walked back from the store with your groceries, and your arms are dropping off. What was so heavy? Well, if you are a milk lover, we probably have the answer. Milk is used in loads of recipes, and it also makes for a really quick and easy drink. But man, is it heavy! It’s easy to see why people buy lots. But, how much does a gallon of milk weigh? Today, we are going to tell you, and you might be surprised by the answer. Read on to find out more.

almond milk on table

How Much Does a Gallon of Milk Weigh

You aren’t interested in science and math? We don’t blame you. The short answer is that a gallon of milk weighs approximately 8.5 pounds. This varies depending on the fat content and what you define as a ‘gallon’. Why, well for that you’ll have to read on to find out.

Milk Weight | A Little Bit of Science

If you thought that all liquids weigh the same, you would be in for a big shock.

Yup, that’s right, science is weird.

Imagine filling a gallon container with water and weighing it. Then you empty it out, fill it with another liquid like, say, milk, and weigh it again.

Here’s what you’ll find. 

The weight will be different.

No, the container hasn’t changed, only the liquid inside. But, here’s the thing. For a given volume, liquids weigh different amounts. For instance, a gallon of fuel weighs 80% of a gallon of water!

This all has to do with each liquid’s molecular density (or to use the scientific term Specific Gravity). Closer packed molecules mean more molecules in a given volume. In basic terms, milk has slightly more molecules and is, therefore, heavier than water!

Wait, what is specific gravity?

Simply put, it is a factor applied to a given weight of water to accurately work out how much another type of liquid weighs. For example: –

  • A liquid with a specific gravity of 0.5 will weigh half that of water
  • A liquid with a specific gravity of 2 will weigh twice as much as water
  • A liquid with a specific gravity of 1.3 will weigh 1.3 times its equivalent volume in water.

With it so far? Good.

How much heavier is milk than water?

Well, milk has a specific gravity of about 1.034. Meaning that it weighs about 1.03 times more than water.

Want that in real terms?

Milk is about 3% heavier than water. So whether you are weighing a cup of milk, a quart of milk, a gallon of milk, or a swimming pool full of milk (get you, Cleopatra), it will always be 3% heavier than water.

See Also: How many ounces in a shot glass

How Much Does Low Fat Milk Weigh?

Here’s where it gets really interesting.

We know what you are thinking.

Low-fat milk makes me lighter (over time and as part of a calorie-controlled diet); therefore, it must be lighter than whole milk?

Right?

Wrong.

Weirdly low-fat milk actually weighs more than whole milk.

Why?

Well, whole milk contains a substantial amount of cream. Want to know what cream is in reality?

Fat.

Fat is slightly less dense than regular milk because it takes up to 10% of the bottle. This means that your whole milk is slightly lighter.

Skim milk doesn’t have this proportion of fat; therefore, it is denser and weighs more… But only slightly more.

We love an excuse to overindulge in cream, and we think that we might just have found a reason. It is for science, yeah, right!

How Much is Gallon of Milk?

This is where it gets even more confusing.

Why?

Because depending on where you are located, a “gallon” can actually mean different things. Putting the weight of milk aside for the moment, let’s delve into this a little deeper.

A gallon is a measure of volume, not weight. And there are two different types of ‘gallon.’

There is the imperial gallon. This is defined as 4546 milliliters. Or, to put it another way, approximately four and a half liters.

There is also the US Gallon. This is 3785 milliliters. An easier way to visualize this is around 3 and three-quarter liters.

That’s a difference of around three-quarters of a liter! Which makes a huge difference when discussing volume weights.

We are going to stick to the US gallon. Why, because, you know, independence.

How Much Does a Gallon of Milk Weigh? | The Math

Ok, there are a few ways you could find out how much a gallon of milk weighs. You could go down to the route of going to the store, buying a gallon of milk, carting it home, pouring it onto a scale set to zero, and writing down the result.

Or.

You could use some basic math and work out the answer on a piece of paper without getting all sweaty… Unless math makes you sweat, of course, and then we can’t help you.

Here’s the math.

1 liter of water (or to put it in exact terms, 1000 milliliters of water, weighs exactly 1 kilogram… so far so good, right?

Like we’ve just told you, a US gallon is 3.78 liters. So a gallon of water weighs exactly 3.78 kilos.

But… 

Milk has a specific gravity of 1.03. meaning it weighs 3% than its equivalent volume in water.

So, the math is 3.78kg x 1.03…

A US gallon of milk, therefore, weighs about 3.9kg.

Math done!

Nope, not quite. We use pounds, not kilos. So, there is a little more math. Let’s convert the weight from kilos to pounds.

A kilo weighs 2.2 pounds. So we multiply the weight in kilos by 2.2.

The answer to how much does a gallon of milk weigh, in pounds?

About 8.5 pounds! That’s pretty heavy!

How much does a gallon of skim milk weigh?

A gallon of skim milk weighs 8.5 pounds.

Conclusion

How much does a gallon of milk weigh? About 8 and a half pounds! While it is simple to work out, it can get pretty confusing depending on whether you use the US, imperial or metric numbers. What’s the most amount of milk you have ever used in a recipe? Let us know in the comments. 

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