If that swanky new vehicle that has caught your fancy is a gas hog, you might want to avert your eyes starting next year, because a new federally mandated label is going to spell it out in big, bold letters.

The first major revision in 30 years of gas-mileage labels on new vehicles will tell you just how much more — or less — you’ll pay for gas over the next five years if you sign on the dotted line and drive that baby home.

In addition to comparing fuel costs with the overall average for new vehicles — “you save $1,850 in fuel costs over five years” — the new labels will provide lots of other information and will use technology to allow car shoppers immediate access to even more data.

“This is about as consumer-friendly as folks around here have ever seen,” said Transportation Secretary Ray LaHood, making the announcement outside his department’s headquarters in Southeast Washington.

This year, the average new vehicle gets 22 miles per gallon at a cost of $10,250 over five years, the Transportation Department said.

The label, which will appear on vehicles designated for the 2013 model year, was developed by the Environmental Protection Agency and the Transportation Department.

Every label will have a “Quick Response” code that can be scanned with available smartphone applications to allow buyers to access additional information, such as customized comparisons of the vehicle they want with others in the same category. Quick Response codes, known as QR codes, are bar codes that steer users to more expansive information online, such as Web tools, video content or multimedia packages.

The new label will also show the current estimated city and highway mileages for the vehicle and the combined average, taking into account that very few people ride exclusively at highway or urban speeds.

It will use average miles driven per year to estimate annual fuel costs, and will provide a rating that combines fuel efficiency with greenhouse gas emissions on a scale of 1 to 10 and another rating for how much smog the vehicle generates. Driving an electric or hybrid model? The label will tell you how much greenhouse gas will be produced by the power plant that generates that electricity.

“It’s the greatest improvement and change in the label in three decades,” said James A. Guest, head of the nonprofit Consumers Union , whose Consumer Reports magazine rates vehicles. “This is going to make fuel economy a priority.”

Guest said a survey by his group found that car buyers are paying more attention to fuel consumption as gas prices have increased by more than a dollar in the past year. He said Consumers Union found that 62 percent of would-be buyers said fuel consumption was a priority, and 73 percent said they would at least consider buying an electric or hybrid vehicle.

LaHood said the new labels will require no additional cost to manufacturers, and the Alliance of Automobile Manufacturers said they welcome it.

“Today’s consumer is a savvy shopper who gathers much information before buying a car, so EPA’s decision to go with informative mpg labels fits consumer needs well,” said alliance spokeswoman Gloria Bergquist.