Fuel Economy Guide: MPG, L/100km & Real-World Savings (2026)

MPG vs L/100km: What’s the Difference?

Miles per gallon (MPG) and liters per 100 kilometers (L/100km) both measure fuel efficiency, but they work in opposite directions. MPG tells you how far a vehicle travels on one gallon of fuel — higher is better. L/100km tells you how many liters a vehicle burns to travel 100 km — lower is better.

The US is one of the few countries still using MPG. Most of the world uses L/100km (source: NIST). If you’re buying a car abroad, comparing specs across markets, or just reading a European review, you’ll need to convert.

How to Convert Between MPG and L/100km

Both units are based on the same physical relationship, so a single constant handles both directions:

MPG to L/100km: divide 235.215 by MPG
L/100km to MPG: divide 235.215 by L/100km

Example: 30 MPG = 235.215 ÷ 30 = 7.84 L/100km

The constant 235.215 comes from converting gallons to liters (1 gallon = 3.78541 L) and miles to kilometers (1 mile = 1.60934 km), then rearranging to put distance per volume into volume per 100 km.

MPG to L/100km Conversion Table

Notice the inverse relationship: as MPG doubles from 15 to 30, L/100km drops from 15.7 to 7.8 — exactly half. Small improvements at low MPG matter more than the same improvement at high MPG.

Real-World Fuel Cost Calculations

Fuel economy ratings look abstract until you attach dollar figures. Here’s how to calculate your annual fuel cost:

Annual fuel cost = (Miles driven ÷ MPG) × Price per gallon

At 15,000 miles/year and $3.50/gallon:

According to fueleconomy.gov, improving from 25 MPG to 35 MPG saves approximately $600/year under these assumptions. Over five years, that’s $3,000 back in your pocket — enough to offset a meaningful chunk of a vehicle’s cost premium.

US vs European Fuel Economy Ratings

US EPA ratings and European WLTP (Worldwide Harmonised Light Vehicles Test Procedure) ratings use different test cycles, so the numbers won’t match for the same car. European figures tend to run higher (better-looking), while EPA numbers are generally closer to real-world driving.

A few key differences:

• US EPA: Separate city and highway ratings. Combined is a 55%/45% weighted average. Tests simulate urban stop-and-go and highway cruising. Values published as MPG.
• European WLTP: Single combined figure in L/100km (or km/L for some markets). Includes low, medium, high, and extra-high speed phases. Generally produces 10–20% better numbers than real-world driving.
• Canadian L/100km: Uses the same EPA test cycles as the US but reports results in liters per 100 km instead of MPG.

When comparing international reviews, always note which testing standard was used. Our fuel economy converter handles the unit math, but the underlying test cycle affects the raw numbers.

Common Vehicles and Their EPA Fuel Economy (2026)

The Toyota Prius holds the record for highest-rated conventional hybrid at 57 MPG combined as of 2026, according to EPA fueleconomy.gov. That’s 4.1 L/100km — less than a third of what a large SUV consumes.

How Driving Habits Affect Fuel Economy

EPA ratings are measured under controlled conditions. Your actual fuel economy depends heavily on how and where you drive.

Speed

According to the US Department of Energy, every 5 mph you drive over 50 mph is equivalent to paying $0.31–$0.50 more per gallon. Aerodynamic drag increases with the square of speed — going 75 mph instead of 65 mph doesn’t just add a little resistance, it adds roughly 30% more drag. Highway hypermilers who stay at 55–60 mph can see 10–20% better fuel economy than rated.

Aggressive Driving

Hard acceleration burns significantly more fuel than smooth, gradual acceleration. Braking wastes the kinetic energy you built up with that fuel. Anticipating traffic and coasting to stops instead of braking hard can improve city fuel economy by 10–40%.

Idling

An idling engine gets 0 MPG. Modern fuel-injected engines use almost no extra fuel restarting versus idling for 30 seconds, so turning off the engine at long stops (more than 60 seconds) saves fuel. Most modern cars handle this automatically with auto stop-start systems.

Tire Pressure

Underinflated tires create more rolling resistance. The DOE estimates that properly inflated tires improve fuel economy by 0.5–3%. Check tire pressure monthly, especially in winter when cold air lowers pressure.

Air Conditioning

Running the AC puts load on the engine and can reduce fuel economy by 5–25% in city driving, according to fueleconomy.gov. At highway speeds above 50 mph, closing windows and using AC is often more efficient than the drag from open windows.

Electric Vehicle Equivalent: MPGe Explained

When the EPA rates EVs and plug-in hybrids, it uses MPGe (miles per gallon equivalent). The unit answers: how many miles could this vehicle travel if it ran on the energy contained in one gallon of gasoline?

One gallon of gasoline contains approximately 33.7 kilowatt-hours (kWh) of energy. So if an EV travels 134 miles on 33.7 kWh, its MPGe rating is 134. The Tesla Model 3 RWD is rated at 138 MPGe — nearly 2.4x more efficient than the 27.3 MPG fleet average.

MPGe does not directly tell you your electricity cost, since electricity prices vary by region. To calculate actual EV running costs, use the formula: kWh per mile × electricity rate per kWh = cost per mile. At $0.15/kWh and 0.25 kWh/mile, that’s $0.04/mile versus roughly $0.14/mile for a 25 MPG car at $3.50/gallon.

Frequently Asked Questions

How do I convert MPG to L/100km?

Divide 235.215 by the MPG value. For example, 30 MPG equals 235.215 ÷ 30 = 7.84 L/100km. The formula works in reverse too — divide 235.215 by L/100km to get MPG. Our fuel economy converter does this instantly.

What is the average MPG for a car in the US?

According to the EPA, the average fuel economy of new cars sold in the US was 27.3 MPG in 2024 (source: EPA Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends Report). That’s up from around 20 MPG in 2000.

How much money can I save by driving a more fuel-efficient car?

At $3.50/gallon and 15,000 miles/year, improving fuel economy from 25 MPG to 35 MPG saves approximately $600/year according to fueleconomy.gov. Over five years, that’s $3,000. The savings increase proportionally with gas prices or annual mileage.

What is MPGe for electric vehicles?

MPGe (miles per gallon equivalent) is the EPA’s measure for comparing electric and plug-in hybrid vehicles to conventional cars. It represents how many miles a vehicle can travel on the energy equivalent of one gallon of gasoline (33.7 kWh). A higher MPGe means greater efficiency. Most EVs rate between 100 and 140 MPGe.

Does driving faster use more fuel?

Yes, significantly. According to the US Department of Energy, every 5 mph you drive over 50 mph is equivalent to paying $0.31–$0.50 more per gallon. Wind resistance (aerodynamic drag) increases with the square of speed, meaning 80 mph burns dramatically more fuel than 60 mph for the same distance.

What is considered good fuel economy?

For a conventional gasoline car, 30+ MPG combined is generally considered good. Above 40 MPG is excellent. The Toyota Prius holds the record for highest-rated conventional hybrid at 57 MPG combined as of 2026. For context, the US fleet average is 27.3 MPG, and large trucks and SUVs typically range from 16–24 MPG.