Miles per US gallon; the standard fuel-economy measure in the United States.
MPG (Imperial)
Miles per Imperial gallon; used in the UK. One Imperial gallon equals 4.546 liters.
L/100km
Liters consumed per 100 kilometers; the metric fuel-consumption standard used in Europe and much of the world.
km/L
Kilometers traveled per liter of fuel; common in Japan and parts of Asia.
MPGe
Miles per gallon equivalent; for electric vehicles. The EPA equates 33.7 kWh to one gallon of gasoline.
EU Efficiency Tier
A-to-F label adapted from EU appliance energy ratings. A+ indicates exceptional efficiency (≥55 MPG US); F indicates very low efficiency (<12 MPG US).
Real-World Examples
Example 1
European family car — 6.0 L/100km
6.0 L/100km → MPG US
= 39.2 MPG US — efficient by US standards, Tier B on the EU label
Example 2
Hybrid annual cost — 51 MPG, $3.50/gal, 12,000 mi
Annual Cost = (12,000 ÷ 51) × $3.50
= $824/year vs. $1,647 for a 25-MPG SUV — $823 saved annually
Example 3
CO₂ comparison — 30 vs 50 MPG
30 MPG → 192 g/km | 50 MPG → 115 g/km
77 g/km difference — 40% lower emissions from the hybrid over the same distance
Understanding Fuel Efficiency Metrics
MPG vs. L/100km: A Non-Linear Relationship
Because MPG and L/100km are inversely related, improving from 15 to 20 MPG saves far more fuel per mile than improving from 35 to 40 MPG. This is why many policy experts prefer L/100km — it scales linearly with actual consumption and makes fuel savings easy to compare across vehicles.
The EU Efficiency Label Explained
The A+ to F rating shown by this converter is adapted from EU appliance energy labelling standards and applied to vehicles by MPG US threshold. A+ (≥55 MPG) covers the best hybrids and EVs. C tier (25–34 MPG) represents the average new car sold in the US. F tier (<12 MPG) includes heavy trucks and exotic performance cars.
Real-World vs. Rated Efficiency
EPA laboratory test-cycle figures often differ from on-road performance by 10–25%. Aggressive driving, cold weather, roof racks, and low tire pressure all reduce real-world efficiency. When comparing vehicles, use the same test standard (EPA, WLTP, or NEDC) and consider your personal driving profile.
Electric Vehicles and MPGe
MPGe (miles per gallon equivalent) allows EVs to be compared on the same scale as combustion vehicles. The EPA defines 33.7 kWh as the energy equivalent of one gallon of gasoline. A Tesla Model 3 Long Range rated at 141 MPGe consumes about 24 kWh per 100 miles — dramatically less than any gasoline vehicle.
Frequently Asked Questions
Why do US and UK MPG ratings differ for the same car?
The US gallon (3.785 L) and Imperial gallon (4.546 L) differ by about 20%. A car rated at 45 MPG Imperial equals roughly 37.5 MPG US. Always check which standard is being used when comparing international specs.
Is L/100km a better unit than MPG?
L/100km scales linearly with fuel consumption, making it easier to calculate actual fuel costs and compare savings. MPG is intuitive in the US but non-linear — a 5 MPG improvement from 15 to 20 MPG saves twice as much fuel as 5 MPG from 30 to 35 MPG.
What does MPGe mean for electric vehicles?
MPGe (miles per gallon equivalent) converts electricity consumption into a gasoline-equivalent metric. The EPA defines 33.7 kWh = 1 gallon of gasoline energy. A Tesla Model 3 at 141 MPGe uses roughly 24 kWh per 100 miles.
How is annual fuel cost calculated?
Annual Cost = (Annual Miles ÷ MPG) × Gas Price per Gallon. For example, driving 12,000 miles at 30 MPG with gas at $3.50/gallon costs $1,400/year. Adjust the Gas Price and Miles/Year fields to match your situation.
How much CO₂ does a gasoline car emit per km?
Burning one liter of gasoline produces approximately 2,310 g of CO₂. This converter uses that constant to compute g/km: CO₂ (g/km) = (L/100km × 2,310) ÷ 100. A 30 MPG car emits about 192 g/km.
What is a good fuel efficiency rating?
The US average is around 28 MPG. Anything above 35 MPG is considered efficient for a gasoline car. Hybrids typically achieve 45–60 MPG. The EU Energy Label used in this converter classifies ≥45 MPG as "A" tier and ≥55 MPG as "A+".