Imperial Gallon to US Gallon Converter
Convert between imperial gallons (UK) and US gallons with precision
Quick Conversions
Conversion Formula
Imperial Gallon to US Gallon
US Gallon to Imperial Gallon
Conversion Example
Convert 10 imperial gallons to US gallons:
10 imp gal × 1.20095 = 12.0095 US gal
Convert 15 US gallons to imperial gallons:
15 US gal × 0.832674 = 12.49011 imp gal
Conversion Reference Table
| Imperial Gallon | US Gallon | Liters |
|---|---|---|
| 1 | 1.20095 | 4.54609 |
| 2 | 2.4019 | 9.09218 |
| 5 | 6.00475 | 22.73045 |
| 10 | 12.0095 | 45.4609 |
| 15 | 18.01425 | 68.19135 |
| 20 | 24.019 | 90.9218 |
| 25 | 30.02375 | 113.65225 |
| 30 | 36.0285 | 136.3827 |
| 40 | 48.038 | 181.8436 |
| 50 | 60.0475 | 227.3045 |
| 75 | 90.07125 | 340.95675 |
| 100 | 120.095 | 454.609 |
Popular Gallon Conversions
Fuel Tank Capacity
A typical UK car fuel tank holds 12-15 imperial gallons, equivalent to 14.4-18 US gallons.
Water Storage
A 50 imperial gallon water tank stores approximately 60 US gallons or 227.3 liters.
Swimming Pool Volume
A 10,000 imperial gallon pool equals roughly 12,010 US gallons or 45,460 liters.
Oil Drums
A 44 imperial gallon drum contains about 52.8 US gallons of liquid volume.
Key Differences Between Imperial and US Gallons
Imperial Gallon (UK)
Volume: 4.54609 liters
Fluid Ounces: 160 fl oz
Used in: United Kingdom, Canada (historically), some Commonwealth countries
US Gallon
Volume: 3.785411784 liters
Fluid Ounces: 128 fl oz
Used in: United States, Latin America, some Caribbean nations
Other Volume Conversions
| From | To | Multiply By |
|---|---|---|
| Imperial Gallon | Liters | 4.54609 |
| Imperial Gallon | US Gallon | 1.20095 |
| Imperial Gallon | US Quart | 4.8038 |
| Imperial Gallon | US Pint | 9.6076 |
| Imperial Gallon | Milliliters | 4546.09 |
| Imperial Gallon | Cubic Meters | 0.00454609 |
| US Gallon | Imperial Gallon | 0.832674 |
| US Gallon | Liters | 3.785411784 |
Step-by-Step Conversion Process
Method 1: Using the Conversion Factor
Step 1: Identify the value in imperial gallons you want to convert
Step 2: Multiply by 1.20095 (the conversion factor)
Step 3: The result is the equivalent in US gallons
Example: 25 imp gal × 1.20095 = 30.02375 US gal
Method 2: Converting Through Liters
Step 1: Convert imperial gallons to liters (multiply by 4.54609)
Step 2: Convert liters to US gallons (divide by 3.785411784)
Step 3: Round to desired precision
Example: 8 imp gal × 4.54609 = 36.36872 L ÷ 3.785411784 = 9.6076 US gal
Frequently Asked Questions
Why are imperial and US gallons different sizes?
The difference stems from historical measurement standardization. In 1824, Britain adopted the imperial gallon based on 10 pounds of water at a specific temperature. The United States retained the earlier English wine gallon of 231 cubic inches, established in 1707. This created a permanent 20% difference between the two systems.
How many US gallons are in one imperial gallon?
One imperial gallon equals exactly 1.20095 US gallons. Conversely, one US gallon equals 0.832674 imperial gallons. The imperial gallon is approximately 20% larger than the US gallon.
Which countries use imperial gallons?
Imperial gallons are primarily used in the United Kingdom. Some Commonwealth countries historically used imperial gallons, though many have transitioned to the metric system. Canada officially uses metric but imperial gallons may still appear in certain contexts.
Which countries use US gallons?
The United States is the primary user of US gallons. Several Latin American and Caribbean nations also use US gallons for fuel and liquid measurements. Most other countries have adopted the metric system using liters.
How do I convert imperial gallons to liters?
Multiply the number of imperial gallons by 4.54609 to get liters. For example, 5 imperial gallons × 4.54609 = 22.73045 liters. This conversion is exact as the imperial gallon is defined as 4.54609 liters.
How do I convert US gallons to liters?
Multiply the number of US gallons by 3.785411784 to get liters. For example, 5 US gallons × 3.785411784 = 18.92705892 liters. The US gallon is defined as exactly 231 cubic inches.
Does fuel economy differ between UK and US ratings?
Yes, significantly. A vehicle rated at 30 miles per gallon in the UK (using imperial gallons) would be rated at approximately 25 miles per gallon in the US (using US gallons) for the same fuel efficiency, due to the 20% difference in gallon sizes.
Are imperial pints and US pints also different?
Yes. An imperial pint is 20 fluid ounces (568 ml), while a US pint is 16 fluid ounces (473 ml). The imperial pint is approximately 20% larger, maintaining the same ratio as gallons.
Practical Applications
Fuel Consumption
When comparing vehicle fuel economy between UK and US markets, always account for the gallon difference. A UK vehicle achieving 40 mpg (imperial) equals approximately 33.3 mpg (US) for the same efficiency.
Recipe Conversions
Cooking recipes from UK sources using gallon measurements need adjustment for US kitchens. One imperial gallon in a recipe equals 1.2 US gallons, which can significantly affect large-batch preparations.
Aquarium Sizing
Fish tank capacities may be listed in either measurement system. A 100 imperial gallon tank holds 120 US gallons, affecting filtration and stocking calculations for aquarium enthusiasts.
Chemical Mixing
Industrial and agricultural chemical mixing ratios must use the correct gallon type. Misinterpreting the measurement system can result in incorrect concentrations with serious consequences.
Historical Context
The gallon has evolved through centuries of trade and measurement standardization. Medieval England used various gallon definitions for different commodities like wine, ale, and corn. The United States adopted the Queen Anne wine gallon of 231 cubic inches in the 18th century, which became the standard US gallon.
In 1824, the British Weights and Measures Act standardized the imperial gallon as the volume of 10 pounds of water at 62°F (277.42 cubic inches or 4.54609 liters). This scientific approach aimed to create a more accurate and reproducible standard. However, by this time, the United States had already established its own measurement system, creating the divergence that persists today.
The 20% difference between imperial and US gallons has led to confusion in international commerce, fuel economy comparisons, and recipe adaptations. While most countries have adopted the metric system, both the UK and US continue using gallons in certain contexts, particularly for fuel retail.
Quick Reference: Common Volumes
| Description | Imperial Gallons | US Gallons |
|---|---|---|
| Small car fuel tank | 10 imp gal | 12 US gal |
| Medium car fuel tank | 13 imp gal | 15.6 US gal |
| Large car fuel tank | 18 imp gal | 21.6 US gal |
| Motorcycle fuel tank | 4 imp gal | 4.8 US gal |
| Small water heater | 25 imp gal | 30 US gal |
| Standard water heater | 42 imp gal | 50.4 US gal |
| Rain barrel | 50 imp gal | 60 US gal |
| Hot tub | 300 imp gal | 360 US gal |