2004 BMW 645ci Convertible: MPG and fuel economy

This page collects every fuel-economy figure the EPA publishes for the 2004 BMW 645ci Convertible. Below you will find the headline combined, city, and highway MPG, the estimated annual fuel cost at three different driving levels, the tailpipe CO₂ emissions, and a full breakdown of the engine and drivetrain. The EPA rates 3 separate variants of this car (different engine, transmission, or drivetrain combinations), and you can compare them side by side in the trims table. If you want to know whether this generation got more or less efficient over the years, the year-over-year table further down covers every model year the EPA has rated.

Fuel economy at a glance

These are the EPA's official ratings for the 2004 BMW 645ci Convertible. The numbers come from a standardised laboratory test cycle and are the same figures that appear on the window sticker of every new car. Real-world mileage varies with driving style, weather, fuel quality, and how heavily loaded the car is.

When the EPA tests several variants of the same nameplate (for example, a front-wheel-drive version and an all-wheel-drive version), each gets its own rating. The figures shown here are the headline variant, taken as the configuration with the best combined MPG. The trims table further down covers all 3 variants side by side.

Combined MPG is a 55/45 weighted blend of the city and highway test cycles. The EPA uses it as the single number you can compare across the entire dataset, including hybrids and EVs (which use the equivalent MPGe figure).

How the 2004 BMW 645ci Convertible compares

The 2004 BMW 645ci Convertible returns 19 combined MPG. Cars in the Subcompact Cars class for the same model year average 19.8 MPG, which puts this car behind the class average by about 4%.

The most efficient car in the Subcompact Cars class for the 2004 model year is the Scion xA at 30 MPG. The bar chart below puts the BMW 645ci Convertible alongside the class best and the class average so you can see the full picture.

For broader context, the average new car of the 2004 model year (across all classes) returns 18.4 MPG. Larger vehicles pull the all-cars average down, so do not use that figure on its own to judge a small car or a hybrid. The full list of the most efficient cars of the 2004 model year is on its own page.

Trim variants rated for 2004

The EPA rates 3 separate variants of the 2004 BMW 645ci Convertible. The differences come from the engine size, transmission type, and drivetrain (front-wheel drive, all-wheel drive, and so on). The same nameplate can land several MPG apart depending on the configuration you actually buy.

Annual fuel cost across driving patterns

The headline annual fuel cost the EPA publishes assumes 15,000 miles of driving per year and a fuel mix of 55% city and 45% highway. The dollar figure is calculated using the EPA's current reference price for premium gasoline, which is $4.61/gallon. EPA updates that reference periodically rather than tracking live pump prices, so treat it as a window-sticker estimate rather than today's pump number.

The table below scales the EPA's number to three common driving patterns. The combined MPG and the reference fuel price stay constant, only the annual mileage changes. To get a current-prices estimate, take your local gas price and multiply by 789.5 gallons (the car's annual consumption at the rated MPG).

Year-over-year MPG for the BMW 645ci Convertible

The EPA has rated the BMW 645ci Convertible across 2 model years, from 2004 BMW 645ci Convertible through 2005 BMW 645ci Convertible. The numbers below are the best combined MPG figure the EPA published for each year, which lets you see when the car was at its most efficient and how recent generations stack up.

Combined MPG has stayed in roughly the same range across the run, hovering close to 19 MPG.

Compare against other Subcompact Cars for 2004

If you are cross-shopping the 2004 BMW 645ci Convertible, the most useful comparison is against the other cars in the Subcompact Cars class for the same model year. The list below shows the highest-MPG peers, ranked from most to least efficient. Click any of them to open its full page.

The Volkswagen New Beetle leads this group at 36 MPG, 17 MPG ahead of the 2004 BMW 645ci Convertible.

Specifications

The 2004 BMW 645ci Convertible runs a 4.4-liter 8-cylinder engine paired with a automatic (s6), sending power through rear-wheel drive.

Engine, transmission, and drivetrain together drive most of the variation in fuel economy across trims. A larger engine moves the car with less effort but burns more fuel. A turbo lets a small engine punch above its weight, often without much MPG penalty. All-wheel drive adds traction and weight, and usually costs a couple of MPG compared with two-wheel drive of the same engine.

Vehicle class

Subcompact Cars

Engine

4.4L 8-cylinder

Transmission

Automatic (S6)

Drivetrain

Rear-Wheel Drive

Fuel type

Premium

Annual petroleum use

15.7 barrels per year

Common questions about the 2004 BMW 645ci Convertible

Quick answers to the questions people most often search for when looking up the 2004 BMW 645ci Convertible.

• Is the 2004 BMW 645ci Convertible fuel efficient?

  It is in line with the rest of the class. The 2004 BMW 645ci Convertible returns 19 combined MPG, and the average car in the Subcompact Cars class for the same model year sits at 19.8 MPG.
• What MPG does the 2004 BMW 645ci Convertible get?

  The EPA rates the 2004 BMW 645ci Convertible at 19 combined MPG, 16 MPG in city driving, and 24 MPG on the highway. Real-world numbers depend on your driving style, the weather, and how loaded the car is.
• How much does it cost to fuel a 2004 BMW 645ci Convertible per year?

  The EPA estimates an annual fuel cost of $3,650 for the 2004 BMW 645ci Convertible. That figure assumes 15,000 miles of driving per year, a 55% city and 45% highway split, and the EPA's published average fuel price for the rated fuel grade.
• Does the 2004 BMW 645ci Convertible require premium gas?

  Yes. The EPA lists the 2004 BMW 645ci Convertible as requiring premium gasoline. Running it on regular can reduce performance and may affect engine warranties, so it is not a recommended way to save at the pump.
• How much CO₂ does the 2004 BMW 645ci Convertible emit?

  Tailpipe CO₂ emissions are 468 g/mi. Multiplied across a typical year of driving (15,000 miles) that works out to about 7,016 kilograms of CO₂.
• What is the difference between the city and highway MPG of the 2004 BMW 645ci Convertible?

  City driving returns 16 MPG and highway driving returns 24 MPG, a gap of 8 MPG. A spread that wide is typical of cars with conventional automatic or manual transmissions, where stop-start city traffic eats more fuel than a steady highway cruise.
• What engine is in the 2004 BMW 645ci Convertible?

  The 2004 BMW 645ci Convertible has a 4.4-liter 8-cylinder engine.
• What transmission and drivetrain does the 2004 BMW 645ci Convertible have?

  The 2004 BMW 645ci Convertible comes with a automatic (s6) transmission and rear-wheel drive.
• How does the 2004 BMW 645ci Convertible compare to the best car in its class?

  The most efficient car in the Subcompact Cars class for the 2004 model year is the Scion xA at 30 combined MPG. The BMW 645ci Convertible returns 19 MPG, a gap of 11 MPG. If you are comparing on fuel economy alone, the class leader is worth a look.
• How much more does the 2004 BMW 645ci Convertible cost in fuel compared to an average car?

  The EPA estimates that over five years, the 2004 BMW 645ci Convertible will cost about $7,500 more in fuel than an average new vehicle of the same model year. The difference accumulates because the car uses more fuel per mile, not because of any one-off charge at the dealership.

Source: U.S. EPA fuel economy dataset. Annual fuel cost figures assume 15,000 miles of driving per year and a 55% city, 45% highway split. Real-world mileage varies with driving conditions, vehicle maintenance, fuel quality, and driver behaviour.