KANSAS CITY — Clutching the $80 ticket you bought months ago, you plow through the sold-out crowd to find your seat at the Sprint Center and drop gratefully into it.

Yikes! It’s a tight squeeze for your derriere.

Maybe it’s all those oversized Cokes and fries you’ve been consuming. Or maybe, just maybe, the problem could be the seat.

It turns out that one-fourth of the Sprint Center’s seats are narrower than seats installed in many other arenas built in the past decade.

Just like Americans, seats have been getting larger in new stadiums, arenas, movie theaters and even cars. After all, middle-age spread is no longer confined to middle age.

But limited space for the downtown arena forced designers to make about 25 percent of the seats, especially in the corners, only 18 inches wide, a Sprint Center spokeswoman said. The rest in the bowl are 19 and 21 inches wide.

“Our goal was to build a world-class arena,” Shani Tate Ross said. “We obviously wanted to go with what was the standard in the industry.”

But the Sprint Center had to be built on only 8 1/2 acres, and that put space constraints on designers.

Kevin Reichard, publisher of Arena Digest, a trade journal, said the 18-inch seats at the Sprint Center were smaller than the 19- to 21-inch seats normally found in newer arenas.

“As a new arena, it is surprising. But they need to cram a lot of seats in a small footprint,” Reichard said. “If you are claustrophobic, it would be very noticeable.”

John Striplin, of Independence, definitely noticed the smaller seats when he attended a Kansas City Brigade game this spring. He said he found them too narrow to sit in.

“I had to stand for the whole game,” he said. “For heavy people and tall people, the seats just are not comfortable.”

There is a way to get a much larger seat at the Sprint Center, but you have to pay a premium: The suites offer 23-inch seats.

That’s now typical, Reichard said.

“Club-level seats are 22 or 23 inches,” he said. “Americans’ butts are bigger than they were a generation ago.”

A federal government project in 2000 found the average American woman had a hip width of 19.7 inches, which was 2.6 inches greater than in 1962. The average American man in 2000 had a hip width of 17.2 inches, which was 1.3 inches bigger than in 1962.

Although the project hasn’t been updated, a government official said last week that the average American weight has increased more than 10 pounds since then, so the average hip width is greater now.

To fit those expanding rears, seats that are 22 inches are ideal, but most arena owners and architects want 20- and 21-inch seats so they can squeeze in more seats, said a representative for Preferred Seating, which is based in Indianapolis.

Janine Gross, office manager for Contour Seats in Allentown, Pa., said 20 inches is typical in newer arenas. Width refers to the actual seat, not the space between armrests.

Here’s how that compares with some newer arenas:

— American Airlines Center in Dallas, which opened in 2001, has 19-, 20- and 21-inch seats, a facility manger said.

— Ford Center in Oklahoma City, which opened in 2002, has 19-, 20-, 21- and 22-inch seats throughout its bowl, spokesman Kim Ransford said. Suite seats are 20 inches or wider.

— Qwest Center in Omaha, Neb., open since 2003, has seats ranging from 19 to 22 inches. To fill the corners, the arena has 23-, 24- and 25-inch seats, along with “very, very few 18-inch seats for the same purpose,” said spokeswoman Rebecca Kleeman.

The silver lining is that Sprint Center seats are bigger than Kemper Arena’s and those at older arenas.

Half a dozen seat manufacturers agree. Seat widths used to run 16 to 17 inches, and the seats didn’t include cushy padding and cup holders.

Indeed, the nearly 25-year-old Kemper Arena has 16- and 17-inch seats.

Kauffman Stadium mainly has seats measuring 19 and 20 inches. However, it has 21-inch seats plus a few 18-inch seats scattered in to make sure the rows are even, an official for the Royals said.

Arrowhead Stadium’s seats range from 18 to 22 inches, with 18-inch seats primarily in the nosebleed sections.

An 11-year Chiefs season-ticket holder, Striplin said he never had a problem with the size of the seats at Arrowhead like he did at the Sprint Center.

“They could have omitted one seat in each row and made it a little more comfortable for everyone,” he said. “I wasn’t comfortable, and the tickets for those seats, even way up high, are expensive.”

But eliminating too many seats could have made the arena — which has a seating capacity of more than 18,000, depending on the configuration — too small for pro hockey and basketball, Reichard said.

He said it made sense to squeeze in the extra seats so the arena was large enough for the NHL and NBA.

He also said smaller seats were needed to ensure the rows lined up properly as sections narrow going toward the floor.

James Tira, of Overland Park, Kan., attended a University of Kansas basketball game last year and was surprised at how narrow the seats were. But, he said, that didn’t change his overall positive view of the arena.

“I’d rather have something like the Sprint Center done, even if it has narrower seats than I would like,” Tira said. “At least something was done.”