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Convert Kilometers per Liter to Gallons per 100 Miles - Fuel Economy Converter

This tool converts fuel economy given in kilometres per litre (km/L) into US gallons consumed per 100 miles (gal/100mi). Gal/100mi expresses how many US gallons a vehicle uses to travel 100 miles—lower values indicate better efficiency.

The conversion combines three fixed relationships: the inverse relation between km/L and litres per 100 km, the kilometre–mile length conversion, and the litre–US-gallon volume conversion. Results are appropriate for vehicle comparisons, fuel-economy reporting, and on-vehicle readouts provided the original measurement is accurate.

Use the examples and FAQ below for guidance about rounding, whether the result uses US or Imperial gallons, and how official testing (EPA/DOE) and calibration practices affect reported figures.

Updated Nov 25, 2025

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Methodology

Step 1 — Convert km/L to L/100 km: L/100km = 100 ÷ (km per L). This expresses fuel use as litres consumed over 100 kilometres.

Step 2 — Convert L/100 km to gallons per 100 miles: multiply L/100km by the factor to change 100 km into 100 miles (100 miles = 160.9344 km) and convert litres to US gallons (1 L = 0.2641720523581484 US gal). Combining constants gives a single conversion: gal/100mi = (100 × 1.609344 × 0.2641720523581484) ÷ (km/L).

Practical note — Because the conversion uses fixed physical constants (metre–mile and litre–gallon), the only source of error is the input measurement (instrument resolution, averaging, or test conditions). For regulatory or lab-grade reporting, follow EPA/DOE test cycle procedures and calibration guidance.

Worked examples

Example 1 — 15.0 km/L: gal/100mi = 42.5143707 ÷ 15.0 = 2.8343 gal/100mi (rounded to 4 decimal places).

Example 2 — 5.0 km/L: gal/100mi = 42.5143707 ÷ 5.0 = 8.5029 gal/100mi (rounded to 4 decimal places).

Further resources

Expert Q&A

Does this output use US gallons or Imperial gallons?

The converter returns US gallons per 100 miles (gal/100mi). Imperial gallons are larger; if you need Imperial gallons per 100 miles, use an Imperial-gallon conversion factor or consult the cited standards to switch the litre→gallon constant.

Why is the conversion not simply reciprocal to miles per gallon?

Miles per gallon (mpg) and gallons per 100 miles (gal/100mi) are related but different displays of fuel efficiency: gal/100mi = 100 ÷ mpg. Converting from km/L to gal/100mi therefore often uses an intermediate mpg step, but we present a condensed constant to avoid rounding loss from multiple conversions.

How many significant digits should I report?

Report results consistent with the precision of your input. For consumer odometer/fuel gauge readings, two to three significant digits are typical; for lab or regulatory reports follow EPA/DOE guidance and provide uncertainty bounds. Avoid implying greater precision than your measurement devices support.

How do testing cycles and real-world driving affect numbers?

Official ratings (EPA/DOE) use standardized laboratory cycles and correction factors. Real-world fuel use can differ due to driving profile, load, tire pressure, and ambient conditions. For regulatory comparability, follow the procedures on government fuel-economy sites referenced below.

How should I verify my vehicle’s reported km/L before converting?

Verify by measuring fuel used over a precisely measured distance (fill-to-fill method), use a certified flow meter if available, and note instrument resolution. Cross-check with manufacturer data and government test-cycle figures for consistency.

Is the constant used here authoritative?

Yes — the constant is derived from exact unit definitions (1 mile = 1.609344 km; 1 US gallon = 3.785411784 L, equivalently 1 L = 0.2641720523581484 US gal). For SI unit definitions and traceability consult NIST and related metrology references listed in citations.

Sources & citations