How many miles per imperial gallon are in one mile per US gallon?

It depends on the value, because this pair is not a simple multiple. Enter your figure above and the tool shows the exact result with the working.

Is the answer exact or rounded?

The calculation itself uses the full stored precision of the defined factor. Only the displayed figure is rounded, and the page also shows a shorter everyday value beside the full one.

Can I check the conversion the other way round?

Yes. The result panel converts the answer straight back into your original unit so you can confirm nothing was lost.

Can I download the result?

Yes — the PDF button produces a branded report with your input, the answer, the formula and the full working.

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Unit Conversions & Measures

Miles per US Gallon to Miles per Imperial Gallon Converter

Convert miles per US gallon to miles per imperial gallon with the exact factor, the working shown step by step and a plain-English explanation.

Your inputs

Change any value to update the result instantly.

Unit Conversions & Measures

Value in miles per US gallonThe US gallon is smaller than the imperial gallon, so US mpg figures are always lower for the same car.

mpg (US)

Miles per Imperial Gallon

9.607599 mpg (UK)

Value in liter per 100 kilometers (internal base unit)

29.401823 L/100 km

Reverse conversion check

9.607599 mpg (UK) = 8 mpg (US)

Rounded for everyday use

9.61 mpg (UK)

The US gallon is smaller than the imperial gallon, so US mpg figures are always lower for the same car. This conversion crosses the US customary and imperial systems, which share unit names but not always the same size.

What this calculator does

Converts a measurement given in mile per US gallons into mile per imperial gallons using the defined conversion factor.

What your result means

The same quantity expressed in mpg (UK) instead of mpg (US). Nothing about the measurement itself changes.

Formula and working

mpg (UK) = convert(mpg (US)) through L/100 km

1
Start with your value
8 mpg (US)
2
Apply the unit relationship
mpg (UK) = convert(mpg (US)) through L/100 km
3
Result
8 mpg (US) = 9.607599 mpg (UK)

Frequently asked questions

Symbols and assumptions

mpg (US): Input unit — mile per US gallon
mpg (UK): Output unit — mile per imperial gallon
L/100 km: Base unit used internally for fuel economy

• Both units measure fuel economy, so the physical quantity is unchanged by the conversion.
• The two units are related by a defined equation rather than a single multiplier, so that equation is applied directly.
• Values are converted through the SI base unit for this quantity rather than pair by pair.

Sources and review

Reviewed 2026-09-22 · Next review 2027-09-22

The International System of Units (SI Brochure), 9th editionBureau International des Poids et Mesures · 9th edition Guide for the Use of the International System of Units (SI), NIST Special Publication 811 — conversion factorsNational Institute of Standards and Technology · 2008 edition

• A unit conversion changes how a number is expressed, not how it was measured — the answer can never be more accurate than the value entered.
• The US gallon is smaller than the imperial gallon, so US mpg figures are always lower for the same car.

Important limitation

This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.

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