2004 BMW 645ci MPG & Specs — Real-World vs EPA, All Trims

Is the 2004 BMW 645ci good on gas?

Real-world MPG vs the EPA number

The EPA figures above come from a standardized dynamometer test, not the open road — real-world MPG typically runs a bit lower depending on your driving, climate and terrain. That's true of every car on this site, old or new.

This 2004 model was originally EPA-tested under the pre-2008 2-cycle method, which didn't account for highway speeds over 60 mph, air-conditioner use, or cold starts. When EPA overhauled the test for model year 2008, city ratings fell by about 12% and highway by about 8% on average industry-wide — and EPA retroactively adjusted every 1984-2007 rating to the stricter standard so old and new cars could be compared fairly. The MPG above is already on that modern scale — the window sticker on this car when it was new likely showed a higher, pre-2008-method number.

At today's AAA national average price — $4.68/gal for premium gas as of 2026-07-05 — the most efficient trim runs about $3,695/year (roughly $308/month, about $24.63 per 100 miles) at the EPA's assumed 15,000 miles/year, using an estimated 789 gallons a year. We don't estimate a cost-per-fill since exact tank size isn't in the public EPA dataset, but the per-100-mile figure scales to any tank. Current national average gas prices →

2004 BMW 645ci trims & fuel economy

2004 BMW 645ci specs

What the EPA test-car listings record for this model year — every combination sold is a row in the trims table above.

Other years of the BMW 645ci

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3 trim(s) · EPA FuelEconomy.gov data retrieved 2026-07-24 · fuel prices AAA national average as of 2026-07-05.