The EPA sorts cars into size classes, and every "best MPG in its class" claim depends on them. The rule is interior volume — passenger space plus luggage space — and nothing else.
| Class | Total interior volume | |
|---|---|---|
| Minicompact | 67.1 cu ft | |
| Subcompact | 96.3 | |
| Compact | 104.1 | |
| Midsize | 113.6 | |
| Large | 125.5 |
Twenty-one cubic feet separates compact from large
That's the whole span between the two ends of the mainstream car market. And because hatchbacks count their cargo area toward the total, they climb classes that saloons of the same footprint don't.
The results:
The 2023–2026 Acura Integra is officially a Large Car. It's a compact hatchback with 120 cubic feet of combined volume.
The 2018 Cadillac ATS-V is officially a Compact Car. A rear-drive performance saloon with 110 cubic feet.
The Hyundai Veloster and Honda Insight are also Compact Cars at 110. So a hatchback the size of a Civic outranks a Cadillac sports saloon.
Why the rule exists
It was written for fuel economy standards, where what matters is how much usable space a vehicle delivers per gallon. From that angle it's sensible: a car that carries more people and luggage on the same fuel is genuinely more efficient at its job, regardless of how long the bonnet is.
It stops being sensible the moment the label gets used as a description of the car, which is what happens on every comparison site and in every review.
Where this actually bites
"Best in class" is a claim about a bucket, not a car. A model can top its class by being classified into a smaller one than it looks.
Cross-class MPG comparisons are meaningless. We found small SUVs averaging 52.6 mpg against 21.9 for minivans — not because they're more efficient but because that's where hybrids get filed.
The classes don't match how anyone shops. Nobody cross-shops an Integra against a Chevrolet Impala, but the EPA puts them in the same group.
What to use instead
Compare specific vehicles, not classes. The combined mpg figure for the exact configuration is the only number that transfers to your fuel bill.
Check interior volume directly if space matters. The passenger and cargo figures are published per model, and they'll tell you more than the class name — especially since a wagon often carries more than the SUV that costs $4,000 more.
Confirm the configuration on a used car. Class, economy and equipment all follow the exact build, and a single model year can span 18 mpg. A VIN check decodes what the vehicle actually left the factory with.
Frequently asked questions
How does the EPA decide vehicle classes?
By interior volume — passenger space plus luggage space — and nothing else. The thresholds run from 67.1 cubic feet for minicompact to 125.5 for large, with just 21 cubic feet separating compact from large.
Why is the Acura Integra classed as a large car?
Because hatchbacks count their cargo area toward total interior volume, giving the Integra 120 cubic feet. The Cadillac ATS-V, a rear-drive performance saloon, measures 110 and is therefore a Compact Car.
Does the class system make sense?
For its purpose, yes — it was written for fuel economy standards, where delivering more usable space per gallon genuinely means a more efficient vehicle. It breaks down when the label is read as a description of the car's size.
Can I trust best-in-class fuel economy claims?
Treat them as claims about a bucket rather than a car. A model can top its class by being classified into a smaller group than it appears, and cross-class comparisons are distorted further by where hybrids get filed.
Denis Kataev is a serial solopreneur and the founder of ForCar. With 15+ years in software engineering and 10 years in SEO, he builds data-driven products end to end — backed by a sharp eye for design. At ForCar he mines proprietary vehicle datasets, turning raw numbers into buying advice you can actually trust.
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