Imperial GPM to US GPM Converter
The Imperial (UK) gallon is 4.54609 liters, while the US gallon is 3.785412 liters. Therefore, 1 Imperial GPM equals 1.20095 US GPM — about 20% larger. This mismatch can cause...
Formula
Source: NIST, UK National Physical Laboratory | Last reviewed: June 7, 2026
Examples
1 GPM (Imp)
= 1.201 GPM (US)
1 Imp GPM = 1.201 US GPM
100 GPM (Imp)
= 120.1 GPM (US)
Where is this used?
Fuel delivery systems, marine engineering, and any project involving equipment from both measurement systems.
Frequently Asked Questions
Why are UK and US gallons different?
The US gallon is based on the Queen Anne wine gallon (231 in³), while the Imperial gallon is defined as 4.54609 L (about 277.42 in³). The UK adopted the Imperial system in 1824.
How do I convert US GPM to Imp GPM?
Divide US GPM by 1.20095. 100 US GPM = 83.27 Imp GPM.
Is the Imperial gallon still used?
The UK officially uses the metric system but Imperial gallons persist in older infrastructure, fuel economy (mpg), and some Commonwealth countries for specific applications.
Reviewed for accuracy
· Last reviewed: June 7, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.