City vs Highway MPG and the Combined Rating (55/45)

The combined MPG on an EPA label is calculated by weighting the city value by 55% and the highway value by 45%. It is the large number on the label because it is meant for quick comparison between vehicles. City and highway values are shown as well, and they matter when your own driving is mostly one or the other.

Key takeaways

• Combined = 55% city, 45% highway. The weights reflect an assumed mix of driving, not a measurement of any one driver.
• The weighting is applied to fuel used per mile, so the combined value is not the plain average of the two MPG numbers.
• The city test is stop-and-go driving with a cold start. The highway test is a free-flowing trip with a warm engine.
• Hybrids can have a city number as high as or higher than the highway number, the reverse of many gasoline cars.

What the city and highway tests represent

According to fueleconomy.gov, the city schedule represents urban driving in which a vehicle is started with the engine cold and driven in stop-and-go rush-hour traffic. It averages 21.2 mph with a top speed of 56 mph over about 11 miles. The highway schedule represents a mixture of rural and Interstate highway driving with a warmed-up engine, typical of longer trips in free-flowing traffic. It averages 48.3 mph with a top speed of 60 mph over about 10.3 miles. The full schedules are laid out in how the EPA tests fuel economy.

Neither schedule is a speed-limit trip. The highway test tops out at 60 mph, so sustained driving at higher speeds is not represented by this test alone. The EPA’s separate high-speed test is one of the five cycles used in building label values.

Why combined is not a simple average

The 55/45 weighting is applied to fuel consumption, meaning gallons per mile, not to the MPG numbers directly. EPA’s regulations describe this as a harmonic average. The reason is physical: you buy fuel by the gallon, so over a mix of driving, the quantity that adds up is gallons used.

A worked example with round numbers: a vehicle rated 20 MPG city and 30 MPG highway.

Step	Calculation	Result
City fuel per mile, weighted	0.55 / 20	0.0275 gallons
Highway fuel per mile, weighted	0.45 / 30	0.0150 gallons
Total fuel per mile	0.0275 + 0.0150	0.0425 gallons
Combined MPG	1 / 0.0425	about 23.5

A plain average of 55% of 20 and 45% of 30 would give 24.5, which overstates the result because the low-MPG city miles burn more fuel. Real label values are computed from test data and rounded for display, so use this example to understand the idea rather than to recompute a label.

Which number should you use

• Mostly urban, short trips: look at the city value. For many gasoline cars it is lower than the highway value.
• Mostly long highway commutes: look at the highway value, keeping in mind the test’s 60 mph top speed.
• A mix, or comparing vehicles in general: use combined.

Hybrids work differently from many conventional cars. Because they can recapture energy when braking and turn the engine off at stops, their city rating can be as high as or higher than their highway rating. Check the label rather than assuming.

The 55/45 assumption in cost estimates

The EPA label’s annual fuel cost uses the combined value, a fixed 15,000 miles a year and a projected fuel price. Gallonly follows the same logic, using the dated EIA prices described in how annual fuel cost is calculated and in the methodology. If your own mix is far from 55/45, the combined value is a less accurate guide to your driving, and the city or highway figure that matches your mix is a better one.

Electric vehicles

For electric vehicles, label range is also built from city and highway results weighted at 55% and 45%, according to the EPA. See EV range explained and kWh per 100 miles and EV efficiency.

A note on label rounding

Label values are whole numbers, so two vehicles with the same displayed combined value can differ slightly underneath. When the difference between two vehicles is only 1 MPG, treat them as close, and compare cost with the fuel cost calculator if the decision matters to you.