Fuel Consumption Converter

Fuel Consumption Converter

Convert between miles per gallon (US), miles per gallon (UK), liters per 100 km, and kilometers per liter. This converter is useful whenever you are comparing vehicles from different countries, interpreting manufacturer specs, estimating trip fuel costs, or trying to understand why the same car appears to have different efficiency ratings in US and European publications.

How Fuel Consumption Conversion Works

The converter uses km/L as the internal base unit for all conversions. The key relationships are:

• MPG (US) to km/L: multiply by 0.425144 (because 1 mile = 1.60934 km, 1 US gallon = 3.78541 L)
• MPG (UK) to km/L: multiply by 0.354006 (because 1 Imperial gallon = 4.54609 L — larger than the US gallon)
• L/100km to km/L: divide 100 by the L/100km value (inverse relationship)
• km/L to L/100km: divide 100 by the km/L value

To go directly from US MPG to L/100km: L/100km = 235.215 / US MPG

To go from UK MPG to L/100km: L/100km = 282.481 / UK MPG

Worked Examples

Example 1 — Converting a manufacturer spec. A European car magazine rates a crossover at 6.8 L/100km under WLTP. What is that in US MPG? Using the formula: 235.215 / (100 / (100/6.8)) = 235.215 / 6.8 = 34.59 US MPG. A US buyer comparing this to EPA-rated vehicles would say this car is roughly equivalent to a 34-35 MPG combined rating.

Example 2 — Estimating annual fuel cost. You drive 15,000 miles per year. One car gets 28 US MPG; another gets 7.5 L/100km. Convert the second car to US MPG: 235.215 / 7.5 = 31.36 MPG. Annual fuel for the first car at $3.50/gallon: (15,000 / 28) x 3.50 = $1,875. For the second: (15,000 / 31.36) x 3.50 = $1,673. The second car saves about $202 per year in fuel.

Example 3 — Japanese spec conversion. A compact car sold in Japan is rated at 20.0 km/L under the WLTC cycle. Converting to L/100km: 100 / 20 = 5.0 L/100km. Converting to US MPG: 20 x (1/0.425144) — or equivalently, 235.215 / 5.0 = 47.04 US MPG. This is a highly efficient vehicle by any market’s standards.

Fuel Consumption Reference Table

When to Use This Converter

• You are comparing cars from different regions where specs are published in different units (US MPG, UK MPG, L/100km, or km/L)
• You want to calculate the annual or per-trip fuel cost difference between two vehicles with ratings expressed in different units
• You are reading a Japanese domestic market spec sheet that lists fuel economy in km/L and need to compare it to US or European figures
• You want to understand why the same vehicle has a higher-looking MPG figure in a UK review versus a US review
• You are tracking your actual fuel consumption over a road trip and want to compare it to the official rated figure in a different unit system

Common Mistakes

1. Assuming UK MPG and US MPG are the same. The UK Imperial gallon is 4.546 L; the US gallon is 3.785 L — a difference of about 20%. A car rated at 40 UK MPG consumes the same fuel as a car rated at only 33.2 US MPG. Never compare UK and US MPG figures directly.
2. Treating the inverse relationship as linear. Because L/100km = 235.215 / US MPG, the relationship is hyperbolic, not linear. Going from 10 to 20 US MPG halves consumption (10 L/100km improvement). Going from 40 to 50 US MPG reduces consumption by only 1.18 L/100km. The MPG scale exaggerates efficiency differences at higher values.
3. Mixing official ratings with real-world driving. EPA (US), WLTP (Europe since 2017), and NEDC (older European) ratings are from controlled lab tests. Real-world consumption is typically 10-20% higher (i.e., worse) due to traffic, temperature, AC use, and driving style. Always add a buffer when estimating fuel budgets.
4. Confusing km/L with L/100km direction. Both are legitimate fuel consumption metrics, but they point in opposite directions. A higher km/L is better (more distance per liter). A lower L/100km is better (less fuel per 100 km). If you see a large number, determine which unit it is before drawing conclusions.

Quick Reference Benchmarks

• Full-size pickup truck (2024): 16-20 US MPG (11.8-14.7 L/100km)
• Average US car (2023 EPA combined): about 26 MPG (9.1 L/100km)
• Average EU passenger car (2022 WLTP): about 6.0 L/100km (39.2 US MPG)
• Toyota Prius (2024): 57 city / 56 highway US MPG (4.1/4.2 L/100km)
• Honda CR-V Hybrid (2024): 43 city / 36 highway US MPG
• Diesel long-haul truck: approximately 6-8 US MPG (29-39 L/100km)
• Hybrid taxi in city driving: roughly 45-55 US MPG (4.3-5.2 L/100km)

Tips

1. For a quick mental conversion from US MPG to L/100km, divide 235 by the MPG number — 235 / 35 = 6.71 L/100km, accurate to within 0.1%
2. UK MPG figures are always about 20% higher than US MPG for the same vehicle — when in doubt, convert both to L/100km before comparing
3. L/100km is better for calculating fuel costs: multiply (distance in km / 100) by L/100km by the price per liter
4. To compare efficiency gains fairly, use L/100km — a drop from 9 to 8 L/100km (saving 1 L/100km) always represents the same absolute fuel saving regardless of starting point
5. Real-world fuel economy is typically 10-20% worse than the official rating; use 85% of the rated figure as a conservative planning estimate
6. For hybrid vehicles, check city and highway figures separately — hybrids often get better city than highway fuel economy, the opposite of conventional vehicles