Convert Kilometers per Liter to Miles per Gallon UK - Fuel Economy Converter
This converter translates fuel economy values expressed in kilometres per litre (km/L) to miles per imperial gallon (mpg UK). It is intended for vehicle owners, fleet managers, and engineers who need a quick, traceable conversion between metric and imperial fuel economy units.
The conversion follows standard unit definitions: kilometres to miles and litres to the imperial gallon. Results are appropriate for display, reporting, and quick engineering checks; check instrument and instrument calibration guidance in the FAQs before using values for regulatory compliance.
Governance
Record f32cd7ce8b98 • Reviewed by Fidamen Standards Committee
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Methodology
We apply fixed, SI-consistent relationships between base length and volume units, then combine them to convert a rate (distance per volume). The method is deterministic and relies on published unit definitions from national metrology and energy agencies.
Kilometres are converted to miles using the internationally accepted metre-to-mile relationship and litres are converted to gallons using the imperial gallon definition. This approach matches guidance from national measurement authorities and energy research groups.
When higher precision is required for regulatory reporting or laboratory work, consult primary sources for the exact constants and perform conversions using the same constants to avoid small discrepancies due to rounding.
Key takeaways
This tool performs a deterministic conversion from kilometres per litre to miles per imperial gallon using standard unit definitions.
For precision-critical work check the exact constants and rounding rules required by the relevant authority and ensure measurement instruments are calibrated.
Worked examples
Example 1: 10 km/L → 10 × 0.62137119223733 × 4.54609 ≈ 28.25 mpg (UK).
Example 2: 5.5 km/L → 5.5 × 0.62137119223733 × 4.54609 ≈ 15.54 mpg (UK).
F.A.Q.
Why is there a difference between UK mpg and US mpg?
The UK (imperial) gallon is larger than the US gallon (1 imperial gallon = 4.54609 L; 1 US gallon = 3.785411784 L). Converting km/L to mpg US uses a different volume factor, so results differ. Use the correct target gallon definition for accurate comparisons.
How many significant digits should I display?
For general use, two decimal places are usually sufficient. For engineering, lab, or regulatory work follow the precision rules required by the governing standard or laboratory protocol. When in doubt, carry full precision in calculations and round only for display.
Can I use this conversion for regulatory reporting?
This converter provides a mathematically correct unit conversion. For regulatory submissions, verify the exact constants and rounding rules required by the reporting body and confirm instrument calibration and test-cycle methodology before submitting data.
My onboard trip computer reports different values than this conversion. Why?
Onboard computers estimate fuel economy from sensor data and may apply smoothing, fuel trims, or manufacturer-specific calibration which introduces differences. This tool performs a pure unit conversion and does not replicate on-vehicle filtering or measurement biases.
How does instrumentation error affect converted values?
Instrument error in distance or fuel volume measurement propagates through the conversion. A relative error in km/L (from sensors or fill-measurements) remains the same percentage when converted to mpg; only absolute numbers change. For critical measurements, rely on calibrated measurement equipment and documented uncertainty budgets.
What constants are used and where do they come from?
This converter uses internationally accepted constants for unit definitions: the kilometre-to-mile factor and the litre-to-imperial-gallon factor. These originate from national metrology institutes and energy research organizations. See citations for authoritative references.
Sources & citations
- NIST Reference on Units and Constants — https://physics.nist.gov/cuu/Units/
- U.S. Department of Energy, Alternative Fuels Data Center — https://afdc.energy.gov/
- National Renewable Energy Laboratory (NREL) — https://www.nrel.gov/
- UK Government guidance on weights and measures — https://www.gov.uk/government/collections/weights-and-measures
- International Organization for Standardization (ISO) unit guidance — https://www.iso.org/
- ISO 80000-3:2019 — Space and time — https://www.iso.org/standard/64974.html
- NIST SP 811 — Guide for the Use of the International System of Units — https://www.nist.gov/pml/special-publication-811
Further resources
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
Record ID: f32cd7ce8b98What changed (latest)
v1.0.0 • 2025-11-28 • 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
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
What changed (latest)
v1.0.0 • 2025-11-28 • 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 28, 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 • 2025-11-28 • 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: 1d5ccc39a65b