How We Calculate Fuel Economy & Cost

This page explains exactly where our numbers come from and how any interpretation on CarMPG is calculated. Our goal is that every figure on the site can be traced back to a public source.

Data source

All fuel-economy, engine, emissions and cost figures are taken from the U.S. EPA fuel-economy dataset at fueleconomy.gov, the official government source that also powers the window-sticker MPG ratings. We reproduce the EPA values without adjustment.

The figures on each page

MPG (city / highway / combined) — EPA estimates from standardized laboratory test cycles.
Annual fuel cost — the EPA estimate based on driving 15,000 miles per year at recent average fuel prices for the vehicle's fuel type.
CO₂ tailpipe — grams of carbon dioxide emitted per mile, as measured by the EPA.
EPA greenhouse-gas score — the EPA's 1–10 rating (10 is best); shown only when the EPA provides one.
Engine, transmission, drive, class — as recorded in the EPA dataset for that configuration.

How we compare a vehicle with its class

When we say a vehicle is "more efficient" or "thirstier" than average, we mean this precisely: we compute the mean combined MPG of every vehicle in the same EPA vehicle class (for example "Compact Cars") across the dataset, then compare the individual vehicle with that average. A difference of 12% or more is described as better or thirstier than the class; anything closer is described as about average. The absolute efficiency band (from "low" to "exceptional") is based on fixed combined-MPG thresholds.

Accuracy and limitations

EPA figures are laboratory estimates. Your real-world mileage will vary with driving style, weather, terrain, fuel grade, vehicle condition and load. Electric vehicles are rated in MPGe, and their running cost depends on local electricity prices rather than fuel. We update the dataset periodically as the EPA republishes it.

If you spot a figure that looks wrong, please tell us via Contact and we will check it against the source.