Fidamen

Convert Miles per Gallon UK to Miles per Gallon - Fuel Economy Converter

This tool converts fuel economy expressed in Miles per Gallon using the United Kingdom (imperial) gallon to the equivalent Miles per Gallon using the United States (US) gallon. It performs a direct unit conversion using the internationally defined gallon-to-litre values so a single numeric input produces a single converted output.

The converter presents the exact conversion factor and common rounded values, practical examples, and guidance on numerical precision and traceability. For engineering or regulatory use, read the accuracy notes and citations to relevant measurement standards.

Updated Nov 10, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record b6863044e3b7 • Reviewed by Fidamen Standards Committee

Interactive converter unavailable for this calculator.

We could not resolve compatible units for this experience. Please verify the slug follows the pattern `from-unit-to-unit-converter`.

Methodology

Conversion is performed by converting both gallon definitions to litres and applying the ratio of litres per imperial gallon to litres per US gallon. This uses the internationally recognized litre definitions and gallon volume specifications published by national standards organizations.

For traceability and measurement best practice we reference standards and guidelines from NIST, ISO and other technical authorities. Results are numeric conversions only and do not attempt to estimate vehicle test-cycle fuel economy or account for measurement uncertainty beyond stated rounding guidance.

Worked examples

Example 1: 40.0 mpg (UK) → 40.0 × 1.200949925 = 48.037997 mpg (US) → display as 48.038 mpg (US) when rounded to three decimal places.

Example 2: 50 mpg (UK) → 50 × 1.200949925 = 60.047496 mpg (US) → display as 60.047 mpg (US) when rounded to three decimal places.

Example 3 (reverse): 30 mpg (US) → 30 ÷ 1.200949925 = 24.977 mpg (UK) → display as 24.977 mpg (UK) when rounded to three decimal places.

F.A.Q.

Which gallon definitions are used for UK and US mpg?

The converter uses the imperial gallon (UK) defined as 4.54609 litres and the US gallon defined as 3.785411784 litres. These volumetric definitions are the basis for the exact conversion ratio.

How accurate is the conversion and how should I round results?

Calculation uses exact published litre values; the conversion factor is approximately 1.200949925. For most consumer uses, rounding to three significant digits is sufficient. For engineering, regulatory, or reporting purposes follow the precision rules required by the applicable standard or agency and include measurement uncertainty where required.

Does this tool account for vehicle test cycles or real-world fuel economy variability?

No. This tool performs only a unit-to-unit conversion of a numeric fuel-economy value. It does not adjust for test-cycle differences, measurement bias, or real-world driving conditions. For regulatory comparisons, consult testing protocols from the relevant authority.

Can I convert in the opposite direction (US to UK)?

Yes. Use the reciprocal of the factor: mpg(UK) = mpg(US) ÷ 1.200949925. Many UIs provide a flip control to swap fromUnit and toUnit.

What standards and organisations support the conversion and measurement practices?

Unit definitions and measurement traceability are maintained by national and international standards bodies including NIST and ISO. Good measurement and reporting practices are recommended by technical organisations such as IEEE and occupational safety guidance from agencies like OSHA where applicable to testing environments.

Are there limits or invalid inputs I should be aware of?

Inputs must be finite non-negative numbers. Very large inputs should be validated by your application to avoid overflow. A zero input yields zero output. Negative values are not meaningful for fuel economy and should be rejected or handled per your data validation policy.

Sources & citations

Further resources

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: b6863044e3b7

What changed (latest)

v1.0.0 • 2025-11-10 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

UI

v1.0.0

Governance

Last updated: Nov 10, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

  • MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
  • MINOR: New features or fields that do not change existing outputs for the same inputs.
  • PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

  • Verify formulas and unit definitions against primary standards or datasets.
  • Run golden-case regression suite and edge-case suite.
  • Record reviewer sign-off with credentials and scope.
  • Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

  • Uses exact unit definitions from the Fidamen conversion library.
  • Internal calculations use double precision; display rounding follows the unit's configured decimal places.
  • Not a substitute for calibrated instruments in regulated contexts.
  • Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-10 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 3ce8f6291a17