Fidamen

Convert Miles per Gallon to Kilometers per Liter - Fuel Economy Converter

This converter translates fuel economy given in miles per gallon (mpg) into kilometers per liter (km/L). It uses standard international unit definitions so results are reproducible and suitable for reporting, planning trips, or comparing vehicles across metric and imperial systems.

By default the tool assumes the common US gallon definition unless you explicitly select or note an Imperial (UK) gallon. The underlying conversion is based on the internationally accepted length and volume unit definitions, not vehicle onboard rounding.

Results are given with practical notes about measurement uncertainty, rounding, and common real-world differences between calculated and onboard computer figures.

Updated Nov 16, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record ba2139f6d24d • 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

We perform a unit-to-unit conversion using the defined relationships: 1 mile = 1.609344 kilometres, 1 US gallon = 3.785411784 litres, and 1 Imperial (UK) gallon = 4.54609 litres. These constants originate from national measurement authorities and international standards.

The conversion calculates kilometres per litre by converting the distance portion (miles → kilometres) and dividing by the volume portion (gallons → litres). For reporting precision we recommend matching the number of significant digits to your measurement method (vehicle trip computer, pump receipts, or laboratory-grade flows).

For regulatory and label contexts, consult official guidance from national agencies on which gallon definition to use and on required rounding rules; our citations include links to government and standards resources.

Key takeaways

This converter uses established unit definitions to convert mpg to km/L reliably. Verify whether the mpg value uses a US or Imperial gallon before converting.

For precise reporting match the rounding and measurement practices to your data source and consult the cited government and standards resources for regulatory requirements.

Worked examples

Example: 30 mpg (US) → km/L. Calculation: 30 × (1.609344 / 3.785411784) ≈ 30 × 0.4251437075 = 12.754 km/L. Report as 12.75 km/L if rounding to two decimal places.

Example (Imperial): 30 mpg (Imperial) → km/L. Use litres per Imperial gallon: 30 × (1.609344 / 4.54609) ≈ 10.62 km/L.

F.A.Q.

Does this converter assume US or Imperial (UK) gallons?

By default the underlying conversion examples use the US gallon (3.785411784 L). If your mpg value is based on the Imperial gallon (4.54609 L) use the Imperial factor. Check your vehicle's country of origin or fuel-economy label to confirm which gallon definition applies.

Why does the onboard trip computer disagree with my manual conversion?

Onboard computers estimate fuel used via fuel-flow sensors and may apply smoothing, filtering, or rounding. Manual conversions use distance and fuel volume measurements (odometer + pump volume) and the exact unit constants; both can differ due to sensor error, calibration, tire size, and driving conditions.

How precise are the conversion constants?

The length and volume constants used here are exact by international convention to the precision published by national metrology institutes. Practical precision should match your input data quality—pump dispensers, odometer resolution, and sample size determine meaningful significant digits.

How should I round results for reporting or labels?

Follow the relevant regulatory guidance for labels in your jurisdiction. When not constrained, round to two decimal places for consumer-facing reports and consider one decimal place for quick comparisons. For engineering or laboratory work, keep full precision until final reporting.

Can I convert L/100 km to km/L or mpg here?

Yes. Convert L/100 km to km/L by taking 100 divided by the L/100 km value. To go from L/100 km to mpg, first convert to km/L then apply the km/L to mpg conversion or use a dedicated L/100 km ↔ mpg converter that applies the same unit constants.

What real-world factors affect measured mpg or km/L?

Temperature (fuel density), fuel composition, pump calibration, tire pressure and diameter, driving style, traffic, and altitude all affect measured fuel economy. For regulatory or lab-grade measurements follow the standardized test procedures published by authorities.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: ba2139f6d24d

What changed (latest)

v1.0.0 • 2025-11-16 • 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 16, 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 • 2025-11-16 • 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: 0b33a4f43cc8