BMW 640i xDrive Convertible
What it costs to keep fuelled
$2,182a year, fuel only
The 2018 BMW 640i xDrive Convertible is EPA-rated at 22 MPG combined (19 city / 28 highway). Over 15,000 miles a year that is about 682 gallons, $2182 a year in fuel, or $0.145 per mile at $3.20/gal.
Across its full 2014–2018 run it averages 22.6 MPG, falling by 1 MPG over 5 model years.
The band is how far one gallon carries it: 22 of the 60 MPG this scale runs to. The square tick is the subcompact cars average, 24.2.
- Fuel, per year
- $2,182 at 15,000 mi
- Per mile
- $0.145
- Per kilometre
- $0.090
- Gallons burned/yr
- 682
1 mile = 1.609344 km · fuel at $3.20/gal, fixed JUL 2026
Test figure — not a road resultSOURCE·US EPA fuel-economy test data·FUEL ASSUMED AT $3.20/GAL FROM JUL 2026·REVIEWED JUL 2026
How this is worked out
- Start from the EPA combined figure for the model year — a laboratory test cycle run to a fixed procedure, not a road result. Where a year sold several engines or drivetrains, the trims are averaged and the trim count is printed beside the row so you can see how much averaging is behind it.
- Fix a pump price. This site keeps one reference price, $3.20 a US gallon, fixed JUL 2026 and printed next to every dollar figure it produces. It is an assumption with a date on it, not a quote — put your own price in.
- Fix an annual distance. Every annual figure on this site uses 15,000 miles a year, roughly the US average. A cost per year with no stated distance is not a number, it is a mood.
- Divide distance by economy for gallons, multiply by price for the year's fuel, divide price by economy for one mile. The per-kilometre line is that last figure divided by 1.609344 — the same money, in the unit most of the world drives in.
- Stop there. No depreciation, no tyres, no insurance, no servicing. This is the fuel line of the ledger and it is labelled as one; depreciation usually dwarfs everything on it.
gallons/yr = miles/yr ÷ MPG fuel $/yr = gallons/yr × $/gal cost $/mi = $/gal ÷ MPG cost $/km = cost $/mi ÷ 1.609344
The full method, the licence note, and what a test figure cannot tell you →
Re-run the ledger at another pump price
Every line above rests on one pump price. Here is the same entry re-costed at six others, because the price is the part that changes while the test sheet stays put.
| Fuel price | Per mile | 10,000 mi/yr | 15,000 mi/yr | 20,000 mi/yr |
|---|---|---|---|---|
| $2.50/gal | $0.114 | $1136 | $1705 | $2273 |
| $3.00/gal | $0.136 | $1364 | $2045 | $2727 |
| $3.20/gal | $0.145 | $1455 | $2182 | $2909 |
| $3.50/gal | $0.159 | $1591 | $2386 | $3182 |
| $4.00/gal | $0.182 | $1818 | $2727 | $3636 |
| $4.50/gal | $0.205 | $2045 | $3068 | $4091 |
| $5.00/gal | $0.227 | $2273 | $3409 | $4545 |
SOURCE·US EPA fuel-economy test data·FUEL ASSUMED AT $3.20/GAL FROM JUL 2026·REVIEWED JUL 2026
The whole service history, sheet by sheet
5 model years on file. Read down the combined column: a nameplate that got heavier shows it here long before any brochure admits it.
| Year | Combined | City | Highway | EPA fuel cost/yr | CO₂ g/mi | Trims |
|---|---|---|---|---|---|---|
| 2018 | 22 MPG | 19 | 28 | $3500 | 396 | 1 |
| 2017 | 22 MPG | 19 | 28 | $3500 | 398 | 1 |
| 2016 | 23 MPG | 20 | 29 | $3350 | 384 | 1 |
| 2015 | 23 MPG | 20 | 29 | $3350 | 385 | 1 |
| 2014 | 23 MPG | 20 | 29 | $3350 | 384 | 1 |
Where a model year offered several engines or drivetrains, the figure is the average across all EPA-tested trims that year — the trim count is shown so you can see how much averaging is involved.
SOURCE·US EPA fuel-economy test data·FUEL ASSUMED AT $3.20/GAL FROM JUL 2026·REVIEWED JUL 2026
Marked against the rest of the subcompact cars bay
Among the 229 subcompact cars models tracked here, the BMW 640i xDrive Convertible ranks 119 on current figures, against a class average of 24.2 MPG — the square tick on the gauge above.
Closest more-efficient alternatives in the same class: Ford Probe (22.3), BMW M240i Convertible (22.5), Mazda MX-6 (22.5), Saab 9-3 Convertible (22.5), Mitsubishi Cordia (22.7).
Tailpipe CO₂ is rated at 396 grams per mile, which works out to roughly 5.9 tonnes a year at 15,000 miles.
Questions asked across the counter
What MPG does the BMW 640i xDrive Convertible get?
The 2018 BMW 640i xDrive Convertible is rated at 22 MPG combined by the EPA — 19 city and 28 highway. Across all 5 model years in the database it averages 22.6 MPG, ranging from 22 to 23 depending on year and trim.
How much does a BMW 640i xDrive Convertible cost in fuel per year?
At 22 MPG and 15,000 miles a year, it burns about 682 gallons — roughly $2182 a year with fuel at $3.20 a gallon, or $0.145 per mile. The EPA's own published annual figure for the 2018 model is $3500.
Has the BMW 640i xDrive Convertible become more efficient over time?
No — it has actually gone backwards, from 23 MPG in 2014 to 22 in 2018. That usually reflects the model growing heavier, more powerful, or moving upmarket rather than the engineering getting worse.
Is the BMW 640i xDrive Convertible efficient for its class?
It ranks 119 of 229 in the Subcompact Cars class on current figures, against a class average of 24.2 MPG. That is 2.2 worse than typical for the class.
Pull another logbook off the same shelf
Same class, nearest economy first — the ones a buyer is genuinely choosing between.
SOURCE·US EPA fuel-economy test data·FUEL ASSUMED AT $3.20/GAL FROM JUL 2026·REVIEWED JUL 2026
Cost per mile, per kilometre and per year are computed at a reference price of $3.20 a gallon over 15,000 miles, fixed JUL 2026 — set your own pump price. Estimates based on official test figures and average fuel prices. Real-world consumption varies with driving style, load, terrain and maintenance.
