Fidamen

Convert Liters per 100 Kilometers to Miles per Gallon UK - Fuel Economy Converter

This converter translates European-style fuel consumption (litres per 100 kilometres) into miles per imperial gallon (UK mpg). The result is useful for drivers, fleet managers, and technical reports that must compare metric consumption figures with UK imperial mpg ratings.

Calculations use the exact international mile (1 mile = 1.609344 km) and the defined imperial gallon (1 imperial gallon = 4.54609 L). These constants are the basis for the conversion factors used by national measurement authorities and transportation agencies.

Updated Nov 20, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 10281eaa621d • Reviewed by Fidamen Standards Committee

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Methodology

Start from the input L/100 km (litres consumed over 100 kilometres). Convert litres per 100 km to miles per imperial gallon by: 1) converting kilometres to miles using 1 mile = 1.609344 km, 2) converting litres to imperial gallons using 1 imp gal = 4.54609 L, and 3) forming the miles-per-gallon reciprocal of litres-per-distance.

The numeric constant used for direct conversion (mpg imperial = K / (L/100 km)) is derived from the product of (100 km × miles per km) and imperial gallons per litre. Using the exact definitions above yields the commonly used factor approximately equal to 282.480936.

Displayed results are rounded for readability; see the FAQs for guidance on precision, instrument error, and regulatory reporting.

Key takeaways

Use this tool to convert L/100 km to miles per imperial gallon using established unit definitions. The single-step conversion uses an exact constants-based factor for reproducible, authoritative results.

For reporting or legal purposes, cross-check rounding rules and measurement uncertainty with your local measurement authority or the documentation of the measuring instrument.

Worked examples

Example 1 — City car: 6.5 L/100 km → mpg (UK) ≈ 282.480936 ÷ 6.5 ≈ 43.46 mpg (UK).

Example 2 — Efficient diesel: 4.0 L/100 km → mpg (UK) ≈ 282.480936 ÷ 4.0 ≈ 70.62 mpg (UK).

Example 3 — Combined cycle: 8.0 L/100 km → mpg (UK) ≈ 282.480936 ÷ 8.0 ≈ 35.31 mpg (UK).

F.A.Q.

Why does the converter use 282.480936 as the factor?

That factor is the result of combining exact definitions: 1 mile = 1.609344 km and 1 imperial gallon = 4.54609 L, then adjusting for the 'per 100 km' denominator. It produces mpg (imperial) when divided into the L/100 km value.

How many decimal places should I trust for real-world measurements?

Instrument and fuel-dispensing tolerances typically limit practical precision. For everyday use, rounding to one or two decimal places is reasonable. For certification or laboratory work, follow the uncertainty and rounding rules of the relevant standard or regulator.

Is UK mpg different from US mpg?

Yes. UK (imperial) gallons are larger (4.54609 L) than US gallons (3.785411784 L), so UK mpg values are numerically higher for the same consumption. Use this converter specifically for imperial (UK) mpg.

Can I use this for legal or compliance reporting?

This tool provides a deterministic unit conversion. For formal reporting, confirm rounding rules, measurement uncertainty, and required reference standards with the regulatory body or laboratory accreditation relevant to your jurisdiction.

What if my input is outside typical vehicle ranges (very low or very high L/100 km)?

The mathematical conversion still applies for any positive numeric input, but extremely low or high values may indicate incorrect data entry or a measurement error. Verify raw measurements before relying on the converted figure.

Where do the conversion constants come from?

The constants come from internationally recognized definitions and national metrology institutions. For the mile-to-kilometre relationship and volume definitions, see the citations below from national measurement authorities and transportation agencies.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: 10281eaa621d

What changed (latest)

v1.0.0 • 2025-11-20 • 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 20, 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 • 2025-11-20 • 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: 7aba64bd26ad