MPG to KM/L: Convert Miles Per Gallon to Kilometers Per Liter

TL;DR — MPG to KM/L Converter

MPG to km/L depends on gallon size: km/L = MPG × 0.425143707 (US) or MPG × 0.354006189 (UK). Conversely MPG = km/L ÷ 0.425143707 (US). L/100 km = 235.214583 ÷ MPG_US = 282.480936 ÷ MPG_UK. Try the Fuel Consumption Converter for instant conversion.

Fuel economy is quoted as miles per gallon in the United States and United Kingdom but as kilometers per liter or liters per 100 kilometers everywhere else. The headline difficulty is that the mpg itself has two meanings because the US liquid gallon is 3.78541 liters while the UK imperial gallon is 4.54609 liters, twenty percent larger. A car rated 30 MPG in the US achieves 36 MPG in the UK with identical fuel burn, and many cross-border shoppers are misled by the larger number. This guide gives the exact formulas for MPG↔km/L and MPG↔L/100 km for both gallon standards, provides tables, worked examples, and authoritative references, so you can compare window stickers, WLTP and EPA figures without error.

Formulas here are dimensionally consistent: 1 mile = 1609.344 meters = 1.609344 km (NIST), 1 US gallon = 3.785411784 L, 1 UK gallon = 4.54609 L, 1 km/L = 2.35214583 US MPG.

Why There Are Two MPG Standards

MPG is defined as miles driven per gallon consumed. Because the numerator mile is identical in the US and UK (both use the international mile), the only difference is denominator gallon. A larger UK denominator inflates the quotient for the same distance and fuel volume. Hence UK MPG = US MPG × 1.200949925. The inverse holds for the metric consumption figure liters per 100 kilometers which is distance-independent. The US EPA reports MPG_US while the UK DVLA and European WLTP report either MPG_UK or L/100 km, creating systematic twenty percent gaps.

The metric alternatives are more physics direct. Kilometers per liter is distance per volume, analogous to MPG but in kilometers. Liters per 100 kilometers is volume per distance, which is the fuel actually burned for a standardized trip. European regulators prefer L/100 km because lower numbers are better and the value scales linearly with carbon emissions. EPA also supplies both on Monroney labels for crossover shoppers.

Exact Formulas: MPG ↔ KM/L ↔ L/100KM

Let MPG_US be US miles per US gallon, MPG_UK be UK miles per UK gallon, km/L be kilometers per liter, L/100km be liters per 100 kilometers.

• MPG_US → km/L: km/L = MPG_US × 0.425143707 (since 1 mi = 1.609344 km, 1 US gal = 3.785411784 L, so 1.609344/3.785411784 = 0.425143707)
• km/L → MPG_US: MPG_US = km/L ÷ 0.425143707 = km/L × 2.352145833
• MPG_UK → km/L: km/L = MPG_UK × 0.354006189 (1.609344/4.54609 = 0.354006189)
• km/L → MPG_UK: MPG_UK = km/L ÷ 0.354006189 = km/L × 2.824809363
• MPG_US → L/100km: L/100km = 235.214583 ÷ MPG_US
• MPG_UK → L/100km: L/100km = 282.480936 ÷ MPG_UK
• L/100km → MPG_US: MPG_US = 235.214583 ÷ L/100km
• L/100km → MPG_UK: MPG_UK = 282.480936 ÷ L/100km

Derivation note: 1 km/L corresponds to 100 ÷ (km/L) L/100km, so conversion between them is reciprocal times one hundred. Many drivers memorize 235.215 as the magic number for US gallons.

Conversion Tables

MPG_US to km/L and L/100km:

• 10 US MPG = 4.251 km/L = 23.521 L/100km
• 20 US MPG = 8.503 km/L = 11.761 L/100km
• 25 US MPG = 10.629 km/L = 9.409 L/100km
• 30 US MPG = 12.754 km/L = 7.840 L/100km
• 35 US MPG = 14.880 km/L = 6.720 L/100km
• 40 US MPG = 17.006 km/L = 5.880 L/100km
• 50 US MPG = 21.257 km/L = 4.704 L/100km
• 60 US MPG = 25.509 km/L = 3.920 L/100km

MPG_UK to km/L and L/100km:

• 10 UK MPG = 3.540 km/L = 28.248 L/100km
• 20 UK MPG = 7.080 km/L = 14.124 L/100km
• 30 UK MPG = 10.620 km/L = 9.416 L/100km
• 40 UK MPG = 14.160 km/L = 7.062 L/100km
• 50 UK MPG = 17.700 km/L = 5.650 L/100km
• 60 UK MPG = 21.240 km/L = 4.708 L/100km

L/100km to both MPG:

• 4 L/100km = 58.804 US MPG = 70.620 UK MPG
• 6 L/100km = 39.202 US MPG = 47.080 UK MPG
• 8 L/100km = 29.402 US MPG = 35.310 UK MPG
• 10 L/100km = 23.521 US MPG = 28.248 UK MPG
• 12 L/100km = 19.601 US MPG = 23.540 UK MPG

Common Pitfalls

Mixing US and UK MPG

The same raw efficiency can be 20 % higher on the UK scale. Automotive journalists sometimes quote UK press release MPG without conversion when reprinting in the US. Always check the publication origin. UK sources should be labeled MPG_imp or MPG_UK, US sources MPG_US.

Confusing km/L with L/100km

Kilometers per liter is larger-is-better like MPG; liters per 100 km is smaller-is-better. Reciprocal confusion leads to buying a less efficient car believing higher is better in both scales. Convert via km/L = 100 ÷ L/100km if you need both presentation styles.

Rounding intermediate

Because 0.425143707 and 235.214583 are irrational from division, rounding to 0.425 and 235 introduces systematic bias over fleet averaging. Keep six significant figures until final reporting to regulators.

Using miles vs kilometers

Some converters mistakenly use 1 mile = 1.6 km approximated. NIST exact is 1 mile = 5280 ft = 1609.344 m exactly. Over 500 km trip the 0.34 % error from 1.6 approximation is 1.7 km misestimation of fuel stop.

Worked Examples

Example 1 — US car window sticker says 28 MPG US. Convert to km/L: 28 × 0.425143707 = 11.904 km/L. Convert to L/100km: 235.214583 ÷ 28 = 8.401 L/100km. For UK audience report 33.63 UK MPG (28 × 1.20095).

Example 2 — European car lists 6.5 L/100km. Convert to US MPG: 235.214583 ÷ 6.5 = 36.19 US MPG, to UK MPG: 282.480936 ÷ 6.5 = 43.46 UK MPG, to km/L: 100 ÷ 6.5 = 15.385 km/L.

Example 3 — Fleet average 14.5 km/L measured in EU. Is that good in US MPG? 14.5 × 2.352145833 = 34.11 US MPG. UK fleet same fuel would be reported 40.96 UK MPG.

How to Convert MPG to KM/L: Step-by-Step

• Step 1 — Identify gallon standard. Check whether the MPG figure is US (EPA) or UK (WLTP Imperial). If source is American EPA, assume US; if British DVLA brochure assume UK.
• Step 2 — Choose target formula. For MPG_US → km/L multiply by 0.425143707. For MPG_UK → km/L multiply by 0.354006189. For MPG → L/100km divide 235.214583 (US) or 282.480936 (UK) by MPG.
• Step 3 — Verify with inverse. Convert result back: km/L × 2.352145833 should return original MPG_US within rounding. If mismatch, you likely used UK factor for US data.

Frequently Asked Questions

What is the formula for MPG to km/L?

For US gallons: km/L = MPG_US × 0.425143707. For UK gallons: km/L = MPG_UK × 0.354006189. The factors derive from 1 mile = 1.609344 km divided by 3.785411784 L per US gallon or 4.54609 L per UK gallon.

Why does US vs UK gallon affect fuel economy numbers?

Because UK gallons are larger, the same car travels the same distance but the gallons denominator is bigger in the UK, so miles per gallon quotient increases by 1.20095. Metric km/L and L/100km avoid this by measuring fuel in litres which are globally uniform per BIPM.

Is higher MPG always better?

Yes for MPG and km/L larger is better, but for the European standard L/100km smaller is better. They are reciprocals: L/100km = 100 ÷ km/L. Always check which scale the regulator uses. EU labels show L/100km and also WLTP CO₂.

What does L/100km mean?

Liters per 100 kilometers is fuel volume needed to travel 100 km. It scales linearly with fuel cost and CO₂ per distance, making fleet aggregation easier than harmonic averaging required for MPG.

Authority: the mile and gallon definitions are in NIST Handbook 44 and the litre definition in the BIPM SI Brochure. Fuel economy testing methodology is documented by the US EPA Fuel Economy.

Tools & reading: compare instantly with our Fuel Consumption Converter and check volume with the Volume Converter, and see our guide MPG to L/100km: How to Convert Fuel Economy Units.

Conclusion

MPG to km/L is not a single formula until you know US versus UK gallon. Memorize 0.425143707 for US and 0.354006189 for UK to get km/L, and 235.214583 for US and 282.480936 for UK to get L/100km. With those reciprocals plus the quick tables above you can translate any EPA, WLTP or DVLA figure accurately, compare window stickers across continents, and avoid the classic twenty percent mistake when switching between imperial and US definitions. Cite litres as the unambiguous base and you will never mis-compare fuel economy again.