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

This converter translates fuel economy in US miles per gallon (mpg) into liters consumed per 100 kilometers (L/100km), the metric standard used in most countries. The conversion is a fixed mathematical relationship based on exact unit definitions for the mile, the kilometer, and the US gallon.

Use this when comparing vehicle economy figures from sources that report mpg (United States) against international ratings reported in L/100km. Results are suitable for quick comparisons, reporting, and unit-normalized calculations for fleet or personal decisions.

Be aware that displayed vehicle economy depends on measurement method (manufacturer test cycles, onboard computers, or user fill-up measurements). This tool converts the numeric unit; it does not adjust for test-cycle differences or real-world driving conditions.

Updated Nov 9, 2025

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Methodology

The conversion uses SI-consistent definitions: 1 mile = 1.609344 kilometers and 1 US gallon = 3.785411784 liters. These exact values are defined by national measurement authorities and referenced by standards organizations.

To convert mpg (US) to L/100km we compute liters consumed per kilometer and scale to 100 km. The conversion factor is constant and derived from the two unit definitions.

This converter uses the direct algebraic relationship; no empirical corrections or test-cycle adjustments are applied. For regulated lab or labeling work, use official agency test cycles and reporting formats from agencies such as the U.S. EPA or DOE.

Worked examples

30 mpg (US) → 235.214583 ÷ 30 = 7.8404861 → 7.84 L/100km (rounded to two decimals).

25 mpg (US) → 235.214583 ÷ 25 = 9.4085833 → 9.41 L/100km.

50 mpg (US) → 235.214583 ÷ 50 = 4.7042917 → 4.70 L/100km.

Further resources

Expert Q&A

Why is a lower L/100km value better?

L/100km measures liters of fuel consumed to travel 100 km; a smaller number means less fuel consumed for the same distance, so lower is more efficient. This is the inverse intuition to mpg, where a larger number indicates better economy.

Does this conversion account for test cycles (EPA/WLTP) or real-world driving?

No. This converter performs a pure unit conversion. Test-cycle protocols (EPA, WLTP) apply standardized driving profiles and laboratory procedures that affect reported numbers. For regulatory or labeling uses, consult the specific agency procedures and test data.

Where does the constant 235.214583 come from?

It is computed as 100 × (3.785411784 L per US gallon) ÷ (1.609344 km per mile). The liter and meter/kilometer definitions are traceable to national measurement institutes.

Should I round results and how many significant digits are appropriate?

For general comparison, two decimal places (e.g., 7.84 L/100km) are typical. For engineering, regulatory, or procurement decisions, follow the precision rules of the governing standard or internal QA procedures; report uncertainty when measurement error exceeds the last reported digit.

How can I measure real-world mpg accurately before converting?

Use the fill‑tank method: fully fill the tank and record the odometer, drive a representative distance, refill to the same level and record liters added and distance traveled. Compute mpg = miles driven ÷ gallons added, then convert. Repeat multiple cycles for average and quantify uncertainty from odometer and pump accuracy.

What measurement limits and errors should I consider?

Common error sources: odometer/GPS distance accuracy, pump metering and temperature effects on fuel volume, partial fills, and human recording error. For small distances, odometer rounding dominates; use longer runs (hundreds of kilometers) and consistent refilling technique to reduce percent error.

Are there different 'mpg' definitions?

Yes. 'US mpg' uses the US liquid gallon (3.785411784 L). Imperial mpg (used historically in some countries) uses the imperial gallon (4.54609 L) and yields a different numeric conversion; ensure you are converting the correct mpg variant.

Can I use this converter for fleet reporting or regulatory submissions?

This tool supplies the unit conversion. For official reporting, follow the regulatory body’s measurement, rounding, and reporting rules (for example, EPA, NHTSA, or regional equivalents). Document methods and uncertainties in any formal submission.

Sources & citations