How much mL makes a gallon?

A gallon is a common unit of measurement used in both the United States and the United Kingdom. But what exactly is a gallon, and how does it convert to milliliters (mL)? Keep reading to find out.

What is a Gallon?

A gallon is a unit of volume or capacity typically used to measure liquids. In the US, a gallon is defined as 231 cubic inches or exactly 3.785 liters. The US gallon is often referred to as the “liquid gallon” to distinguish it from the smaller US dry gallon which is equal to 4.405 liters or 268.8025 cubic inches.

In the imperial system used in the UK, a gallon is defined as the volume of 10 pounds of water at 62°F. This amounts to approximately 4.546 liters or 277.42 cubic inches.

So in summary:

  • 1 US liquid gallon = 231 cubic inches = 3.785 liters
  • 1 Imperial gallon (UK) = 277.42 cubic inches = 4.546 liters

Knowing the different gallon definitions is important when converting between gallons and other units like mL.

What is a Milliliter?

A milliliter (mL) is a metric unit of capacity that is equal to one thousandth of a liter. Since a liter is defined as the volume of one kilogram of water, a milliliter is 1/1000 of that volume.

Some key facts about the milliliter:

  • 1 mL = 0.001 liters
  • 1 mL is equivalent to about 0.033814 fluid ounces
  • 1 mL is the same as 1 cubic centimeter (cm3)

Milliliters are commonly used to measure small amounts of liquids like medicines, chemicals, or food ingredients. For example, many medicine bottles contain mL markings to allow measuring out the correct dose.

Converting Between Gallons and Milliliters

Now that we understand the definitions of gallons and milliliters, how do we convert between these units?

There are a few key conversion factors to remember:

  • 1 US gallon = 3785 mL
  • 1 Imperial gallon = 4546 mL
  • 1 mL = 0.00026417 US gallons
  • 1 mL = 0.00021996 Imperial gallons

So for example, to convert 5 US gallons to milliliters we would calculate:

5 gallons x 3785 mL/gallon = 18,925 mL

And to convert 2000 mL to Imperial gallons:

2000 mL x 0.00021996 Imperial gallons/mL = 0.43992 Imperial gallons

Let’s look at some more examples of converting between gallons and mL:

Gallons Milliliters
2 US gallons 7570 mL
10 Imperial gallons 45460 mL
5000 mL 1.321 US gallons
3250 mL 0.716 Imperial gallons

To make these unit conversions, we simply multiplied the original quantity by the appropriate conversion factor. Handy converters are also available online for quickly converting gallons, liters, and milliliters.

Comparing Milliliters and Gallons

Looking at the conversion factors above, we can see that:

  • There are about 3785 milliliters in 1 US gallon
  • There are approximately 4546 milliliters in 1 Imperial gallon

This means an Imperial gallon contains about 20% more volume than a US gallon. Keep this difference in mind when converting between the two gallon definitions.

We can also compare relative sizes and capacities:

  • 1 liter = 1000 mL
  • 1 US gallon = 3.785 liters = 3785 mL

So a liter is a bit more than 1000 mL, while a US gallon equates to nearly 3800 mL. Looking at it another way:

  • 1 fluid ounce = about 30 mL
  • 1 US gallon = 128 fluid ounces
  • So a gallon is equivalent to over 3,700 mL!

As you can see, a gallon represents a much larger volume than a milliliter. Some visualization may help put this in perspective.

Unit Visualization
1 mL A single drop of water
30 mL (1 fluid ounce) About 1 shot or cough syrup dose
240 mL (1 cup) A small yogurt container
3785 mL (1 US gallon) A large milk or juice jug

This helps put into perspective the large size and volume of a gallon compared to a tiny milliliter!

When to Use Gallons vs. Milliliters

In summary, here are some general guidelines on when gallons or milliliters are most appropriately used:

  • Milliliters are best for measuring very small liquid volumes, like in medical, chemical, or cooking applications.
  • Gallons are better suited for measuring large volumes like the capacity of gas tanks, water heaters, pools, etc.
  • In the US, gallons are commonly used to measure fuel, milk, paint, etc. while recipes may use gallons, quarts, cups, ounces, and milliliters.
  • In countries like Australia, Canada, and the UK, gallons may be less common than liters and milliliters for most liquid measurements.
  • Converting between gallons and milliliters allows comparing liquid amounts across different units and measurement systems.

The key is using the appropriate unit – gallons or milliliters – for the specific application and volume being measured. Paying attention to the type of gallon definition being used (US or Imperial) is also important during any unit conversions.

Fun Facts About Gallons and Milliliters

Here are some interesting fun facts and trivia about gallons and milliliters:

  • A US gallon of water weighs over 8 pounds.
  • There are approximately 20 drops of water in 1 milliliter.
  • The US gallon volume definition is based on the volume of grain rather than water.
  • A swimming pool typically holds 20,000 – 50,000 gallons of water.
  • Humans consume on average over 3,700 mL (1 gallon) of water per day.
  • The gas tank of a typical sedan holds 12-18 gallons of fuel.
  • The earliest known reference to a gallon size was in 1228 in Britain referring to a 4.5 liter wine gallon.
  • Early definitions of gallons, cups, and fluid ounces were based on commodity volumes like wine, wheat, or barley.

Hopefully these fun gallon and milliliter facts gave you a few interesting tidbits to share!


In summary, a US gallon equals 3,785 mL while an Imperial gallon is equivalent to 4,546 mL. Converting between gallons and milliliters simply requires multiplying by the appropriate conversion factors. Gallons are best for measuring large volumes and capacities while milliliters are ideal for smaller liquid amounts. Being familiar with gallons and milliliters allows easy conversion between these common units of fluid measurement.

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