Fuel Consumption Unit Converter
Convert between fuel-economy units — L/100km, km/L, mpg (US), mpg (UK), L/km — with the exact reciprocal formulas used by ECE R101 and the US EPA. Read the FAQ first: fuel consumption uses inverse math, not a single linear factor.
Reviewed by WuTools Engineering Team · Last updated
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Why is fuel consumption mathematically different from other unit conversions?
Most unit conversions are linear — multiply by one factor and you are done. Fuel consumption is the rare exception, because the world has not agreed whether to measure "how much fuel for a given distance" or "how much distance for a given fuel". The European convention is the first (volume per distance: L/100km, L/km), the North American and historically British convention is the second (distance per volume: mpg, km/L). Converting between the two families requires a reciprocal — a 1/x relationship — not a multiplication.
The exact formulas are: L/100km = 235.21458 ÷ mpg(US) = 282.48094 ÷ mpg(UK) = 100 ÷ (km/L). The constants come from unit definitions: 1 mile = 1.609344 km (exact), 1 US gallon = 3.785411784 L (exact), 1 UK Imperial gallon = 4.54609 L (exact). The interactive converter at the top of this page applies a linear approximation calibrated near the everyday range (≈10 L/100km) — for cross-family conversions consult the formulas below or use the reference table for typical vehicles.
The fuel-consumption units, explained
Liter per 100 kilometers (L/100km) — the European standard
L/100km is the official metric in the European Union, the ECE WLTP type-approval procedure, and most of Asia. It is intuitive for budget planning: 7 L/100km × 1.80 €/L = 12.60 € per 100 km. Lower numbers are better — a hyper-efficient hybrid sits at 4 L/100km, an SUV at 9–11 L/100km, a truck at 30+ L/100km. It is volume-per-distance, the inverse mathematical direction from mpg or km/L.
Kilometer per liter (km/L) — common in Brazil, Japan, India, Vietnam
km/L flips L/100km: km/L = 100 / (L/100km). So 5 L/100km = 20 km/L; 10 L/100km = 10 km/L. Brazil reports vehicle efficiency in km/L for each fuel — gasoline and ethanol — because flex-fuel cars deliver different km/L on the two fuels. Higher numbers are better. An economical small car returns 18–22 km/L on gasoline and 12–15 km/L on ethanol due to ethanol's lower energy density.
Mile per gallon (US) — the American convention
mpg(US) uses the US Customary gallon of 3.785411784 L. Conversion to L/100km is the famous formula 235.21458 / mpg(US). The CAFE standard targets 49 mpg(US) by 2026 for passenger cars (= 4.8 L/100km). A 2025 Toyota Prius achieves 57 mpg combined (= 4.13 L/100km); a Ford F-150 V8 returns 18 mpg (= 13.07 L/100km). Higher is better.
Mile per gallon (UK / Imperial) — pre-2010 British convention
mpg(UK) uses the larger Imperial gallon of 4.54609 L. Conversion: L/100km = 282.48094 / mpg(UK). UK road tests in the 1990s and early 2000s quoted mpg(UK), so old British car magazines and brochures should be read carefully. UK manufacturers since 2010 generally print L/100km alongside or instead of mpg(UK).
Liter per kilometer (L/km) — for heavy commercial vehicles
Large trucks and buses can consume 0.30–0.45 L/km (= 30–45 L/100km), so L/km gives a tidier number. Logistics dispatchers price routes in € per km using L/km × fuel price directly. It is just L/100km × 1/100, not a fundamentally different convention.
Real-world fuel consumption — typical figures
- Compact city car (gasoline, modern): WLTP combined: 5–7 L/100km = 14–20 km/L = 33–47 mpg(US) = 40–56 mpg(UK). Examples: VW Polo 1.0 TSI ≈ 5.5 L/100km; Honda Jazz 1.5 i-MMD ≈ 4.6 L/100km.
- Compact hybrid (HEV): Combined: 3.5–5 L/100km = 20–28 km/L = 47–67 mpg(US). Examples: Toyota Prius ≈ 4.1 L/100km, Honda Civic e:HEV ≈ 4.5 L/100km.
- Mid-size SUV (gasoline): Combined: 8–11 L/100km = 9–12 km/L = 21–29 mpg(US). Examples: Toyota RAV4 2.5 ≈ 7.4 L/100km, Honda CR-V Turbo ≈ 8.1 L/100km.
- Pickup truck (large, V6 or V8): Combined: 11–16 L/100km = 6–9 km/L = 14–22 mpg(US). Examples: Ford F-150 V6 EcoBoost ≈ 11.2 L/100km, Ram 1500 V8 ≈ 14.7 L/100km.
- Class-8 semi truck (diesel): Combined: 30–42 L/100km = 2.4–3.3 km/L = 5.6–7.8 mpg(US). Modern aerodynamic tractors loaded to 36 t can reach 28 L/100km on highways.
- Motorcycle (250–600 cc): Combined: 3–5 L/100km = 20–33 km/L = 47–78 mpg(US). 125-cc commuters can reach 50–60 km/L.
- Aviation (per passenger-km): Modern narrow-body airliners (A320neo, 737 MAX): 2.2–2.6 L/100passenger-km. Long-haul wide-body fully loaded: 2.8–3.4 L/100passenger-km. Quoted differently — by passenger-kilometer — but mathematically the same fuel-per-distance idea.
Reference table — typical values across units
| Unit | Approximate L/100km |
|---|---|
| 1 L/100km (Liter per 100 kilometers) | 1 Pa |
| 1 km/L (Kilometer per liter) | 10 Pa |
| 1 mpg (US) (Mile per gallon (US)) | 23.521458 Pa |
| 1 mpg (UK) (Mile per gallon (UK)) | 28.248094 Pa |
| 1 L/km (Liter per kilometer) | 100 Pa |
Frequently asked questions about fuel-consumption units
How do I convert L/100km to mpg(US) and back?
Use the reciprocal formula: mpg(US) = 235.21458 / L_100km, and L_100km = 235.21458 / mpg(US). The constant 235.21458 = 100 × 2.35214583 = 100 × (1.609344 km/mile) / (3.785411784 L/gallon)⁻¹. So 8 L/100km = 235.21458 / 8 = 29.4 mpg(US). And 30 mpg(US) = 235.21458 / 30 = 7.84 L/100km.
Are mpg(US) and mpg(UK) the same?
No. The UK Imperial gallon is 4.54609 L, while the US gallon is 3.785411784 L — the Imperial gallon is about 20% larger. Therefore the same car shows higher mpg in the UK than in the US. Example: a car rated 30 mpg(US) is 36.0 mpg(UK). The conversion is mpg(UK) = 1.20095 × mpg(US).
Why does my car's display switch between km/L and L/100km?
Many modern vehicles let you choose either, because each is helpful for different scenarios. km/L is intuitive when planning a trip with limited fuel ('I have 10 L, can I make 200 km?'). L/100km is intuitive when budgeting fuel for a known distance. Both are correct measurements of the same underlying physics.
What is considered good fuel economy in 2026?
For a passenger car, the modern benchmarks are: excellent below 5 L/100km (above 47 mpg US, above 20 km/L), good 5–7 L/100km (33–47 mpg US, 14–20 km/L), average 7–9 L/100km, thirsty above 10 L/100km. EVs and PHEVs are reported in MPGe or kWh/100km on a different basis.
Why is fuel economy worse in the city than on the highway?
City driving involves frequent acceleration from stop, low average speed, and engine idling — none of which moves the car forward. Highway driving keeps the engine in its efficient cruise band. A typical gasoline car gets 20–30% better fuel economy on the highway. Hybrids invert the pattern: regenerative braking captures stop-and-go energy, so HEVs are more efficient in the city.
Why doesn't my actual fuel consumption match the official number?
Official figures (WLTP, EPA) come from a standardized lab test cycle. Real-world variables — speed, weather, tire pressure, traffic, cargo, AC, driver behavior — typically push consumption 10–25% higher. The 2017 transition from NEDC to WLTP narrowed but did not close this gap.
Does fuel type affect km/L on a flex-fuel car?
Yes — significantly. Ethanol contains about 33% less energy per liter than gasoline, so a flex-fuel car burning E100 (pure ethanol) typically gets 30% fewer km/L than on E10/E20 gasoline. Brazilian flex-fuel cars are advertised with separate km/L figures for each fuel.
How do I convert km/L to mpg directly?
mpg(US) = km/L × 2.352146 and mpg(UK) = km/L × 2.824809. Inverse: km/L = mpg(US) / 2.352146 = mpg(UK) / 2.824809. Example: 15 km/L × 2.352146 = 35.3 mpg(US).
Is the converter on this page accurate for cross-family conversions?
The interactive converter uses linear factors calibrated near 1 unit value, so cross-family conversions (L/100km ↔ km/L or mpg) lose accuracy outside the typical 5–15 L/100km range. For exact answers, apply the reciprocal formulas in the previous answers, or switch to a dedicated converter page (linked below) that uses the proper inverse math.
What about EVs — what unit do they use?
Electric vehicles are reported in kWh/100km (Europe), Wh/km (technical specs), or MPGe (US EPA — equivalent miles per gallon, where 33.7 kWh = 1 gallon-of-gasoline equivalent). A modern EV consumes 14–20 kWh/100km, which is roughly equivalent to 1.5–2.2 L/100km of gasoline by energy content.
References
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI)
- BIPM SI Brochure (9th edition, 2019)
- ISO 80000-3:2019 — Quantities and units, Part 3: Space and time
- UNECE Regulation No. 101 — CO₂ emissions and fuel consumption measurement
- US EPA Fuel Economy Test Procedures (40 CFR Part 600)
Dedicated converter pages
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