Gallon calculator

What is a gallon?

A gallon is a common unit of measurement for liquid volume used mostly in the United States and, to a limited extent, in the United Kingdom. However, not all gallons are equivalent — different regions adopted different standards over time.

There are three primary types of gallons:

1. US fluid gallon = 231 cubic inches = 3.78541 liters
2. US dry gallon = 268.8025 cubic inches = 4.40488 liters
3. Imperial (UK) gallon = 277.4194 cubic inches = 4.54609 liters

Because these vary significantly, it is essential to specify which gallon is being used when performing any conversion.

The gallon calculator allows users to convert between gallons and other volume units such as liters, milliliters, cubic meters, quarts, pints, and cups. It can also convert gallons to weight (kilograms or pounds), considering the density of the substance being measured. This makes it a versatile tool for fields like cooking, chemistry, agriculture, and industrial processes.

Formula

The core formulas depend on whether the conversion involves volume only or both volume and weight.

1. Volume conversion formula

To convert gallons to liters (the most common metric counterpart):

$$V_{L} = V_{gal} \times C$$

Where:

• $V_{L}$ = volume in liters
• $V_{gal}$ = volume in gallons
• $C$ = conversion coefficient depending on gallon type

The coefficients are:

• For US fluid gallon: $C = 3.78541$
• For US dry gallon: $C = 4.40488$
• For Imperial gallon: $C = 4.54609$

2. Weight conversion formula

To convert gallons into weight, you must include the density $\rho$ of the liquid:

$$m = V_{gal} \times C \times \rho$$

Where:

• $m$ = mass (in kilograms if $\rho$ is in kg/L)
• $V_{gal}$ = volume in gallons
• $C$ = gallon-to-liter conversion factor
• $\rho$ = density of the material (kg/L or g/cm³)

If working with imperial units (pounds per gallon):

$$W_{lb} = V_{gal} \times \rho_{lb/gal}$$

This version is convenient when density data is given directly in pounds per gallon. Note that the term “weight” in this context is used to denote mass, not gravity.

Common conversions

• 1 US fluid gallon = 3.78541 L
• 1 US dry gallon = 4.40488 L
• 1 Imperial (UK) gallon = 4.54609 L
• 1 gallon = 128 US fluid ounces
• 1 gallon = 8 pints = 4 quarts
• 1 liter = 0.264172 US gallons

In reverse conversion from liters to gallons:

$$V_{gal} = \frac{V_{L}}{C}$$

where $C$ corresponds to the type of gallon desired.

Examples

Example 1: Converting US gallons to liters

A tank contains 15 US fluid gallons of water.

$$V_{L} = 15 \times 3.78541 = 56.78115\ L$$

So, the tank holds approximately 56.78 liters.

Example 2: Converting gallons to kilograms

Suppose you have 3 Imperial gallons of olive oil, with a density of $\rho = 0.918\ kg/L$.

$$m = 3 \times 4.54609 \times 0.918 = 12.51913\ kg$$

Hence, 3 Imperial gallons of olive oil weigh approximately 12.52 kilograms.

Example 3: From gallons of gasoline to pounds

If gasoline has a density of 6.073 lb/US gal, then 10 gallons weigh:

$$W_{lb} = 10 \times 6.073 = 60.73\ lb$$

Thus, 10 gallons of gasoline weigh about 60.73 pounds.

Example 4: Converting milk volume to cups

1 US gallon = 16 US cups.
For 2.5 gallons of milk:

$$16 \times 2.5 = 40\ cups$$

That’s 40 cups of milk.

Historical background

The confusion surrounding gallons dates back to the 17th century. Each type of liquid — wine, ale, or corn — was originally measured using different gallon definitions in Britain. To standardize measurement, the British Weights and Measures Act of 1824 established the imperial gallon based on 10 pounds of pure water at 62°F (17°C).

In the US, earlier systems remained unchanged, leading to the US fluid gallon derived from the old English wine gallon. This is why today’s gallon conversions differ between the US and UK. Understanding these differences is crucial for global trade, scientific measurement, and culinary precision.

Notes

1. When converting to weight, always use the correct density. For example:
   • Water = 1.000 kg/L
   • Milk ≈ 1.03 kg/L
   • Olive oil ≈ 0.918 kg/L
   • Gasoline ≈ 0.745 kg/L
2. For temperature-sensitive substances, density may vary; thus, conversions may slightly differ with temperature changes.
3. Always specify which type of gallon (US fluid, US dry, or Imperial) you are using. In most everyday situations, especially in the US, the default unit is US fluid gallon.

Frequently Asked Questions

How many liters are there in 5 US gallons of water?

$$V_{L} = 5 \times 3.78541 = 18.92705\ L$$

There are 18.93 liters in 5 US gallons.

What is the weight of 2 US gallons of honey?

Assuming honey has a density of approximately 1.42 kg/L:

$$m = 2 \times 3.78541 \times 1.42 = 10.75\ kg$$

Therefore, 2 US gallons of honey weigh around 10.75 kilograms.

How many US gallons are equal to 50 liters?

$$V_{gal} = \frac{50}{3.78541} = 13.2086$$

So, 50 liters ≈ 13.21 US gallons.

How to convert 4 Imperial gallons to quarts?

An Imperial gallon = 4 Imperial quarts.

$$4 \times 4 = 16$$

Thus, 4 Imperial gallons equal 16 Imperial quarts.

How much does 1 Imperial gallon of water weigh?

Since the imperial gallon was defined as the volume of 10 pounds of water, 1 Imperial gallon of water weighs 10 pounds (≈ 4.546 kilograms).