What is 40 mpg imperial in US mpg?

40 imperial mpg is about 33.31 US mpg. Multiply imperial mpg by 0.8327 to convert.

Why does the same car show a higher mpg in the UK than in the US?

The UK figure runs about 20% higher because an imperial gallon (4.54609 L) is larger than a US gallon (3.785411784 L). For example, 30 US mpg is about 36.03 imperial mpg.

A UK ad says 55 mpg. What would a US buyer compare it to?

55 imperial mpg is about 45.80 US mpg. Compare that figure against US mpg ratings.

How do I convert US mpg to imperial mpg?

Multiply by about 1.201. For 30 US mpg that gives about 36.03 imperial mpg, and 50 US mpg gives about 60.05. More converters are in the fuel economy category.

MPG (Imperial) to MPG (US) Converter

Enter a value to instantly convert between fuel economy units.

From

Precision4 dp

1 MPG (Imperial) = 0.8327 MPG (US)

Key Formulas

MPG (US) → Liters per 100km

L/100km ≈ 235.215 / mpg

Liters per 100km → MPG (US)

mpg ≈ 235.215 / L/100km

Km per Liter → MPG (US)

mpg = km/L × 2.35215

MPG (US) → Km per Liter

km/L = mpg × 0.425144

Formula

mpg = mpg imp × (235.214583333 / 282.480936332) (constants shown rounded)

Multiply imperial mpg by 0.83267 to get US mpg. The ratio is 3.785411784 L per US gallon divided by 4.54609 L per imperial gallon. The mile is the same on both sides, so only the gallon changes the number. A UK car rated 30 mpg imperial earns about 24.98 mpg on a US scale, and 50 mpg imperial becomes about 41.63 mpg. Shoppers use this conversion to compare British ratings with EPA figures. The imperial gallon holds about 20% more fuel, which is why UK numbers look higher.

Source: NIST named gallon and mile definitions; reciprocal fuel ratio derived from them

Reviewed by the Convert Calc editorial team · Last reviewed: 2026-10-06 · see our methodology

Frequently Asked Questions

Real-World Examples

Example: UK car at 40 mpg, shown as a US mpg figure.

40 mpg imp = 33.30696738515955 mpg

Example: UK ad figure of 55 mpg, compared with US ratings.

55 mpg imp = 45.79708015459438 mpg

Example: used UK import at 30 mpg, in US mpg.

30 mpg imp = 24.980225538869668 mpg

Example: UK hybrid at 65 mpg, restated in US mpg.

65 mpg imp = 54.12382200088428 mpg

mpg to l per 100km l per 100km to mpg kml to mpg mpg to kml

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