At 1.73 metres tall, Eddie Santos is about average size, but on a recent flight from Los Angeles to Washington a trip to the plane's lavatory left him feeling like Gulliver in the land of Lilliputians.

It was a tight fit.

"I had to twist my shoulder just to get in," he said. "It was uncomfortable."

Flier Melody Arganda was able to squeeze inside, but she said the space was so narrow her thighs brushed against the walls.

"Absolutely ridiculous," hrumphed the retired teacher from Riverside, California. "If I were any bigger, I wouldn't have fit."

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Flying has become a game of inches, with airlines trying to squeeze as many passengers as possible on planes. They have made seats smaller, shrunk legroom and now, as Santos and Arganda discovered on a recent US cross-country flight, made the bathrooms so small an average-size person feels squeezed.

SATTAPAPAN TRATONG/123RF "I had to twist my shoulder just to get in," said Eddie Santos.

On some of the newer planes flown by American, Delta and United airlines, the bathrooms in coach are just 61 centimetres wide. For comparison, that's roughly the width of the average dishwasher.

By comparison, the average porta-potty is roughly 86cm wide.

According to the manufacturer, the new-style bathrooms free up enough space to fit six more passengers onboard.

Delta was the first to introduce the smaller bathrooms in 2014, but the shift gained more attention late last year when American began using new jets equipped with the tiny lavatories. United debuted theirs in June.

Joseph "Pep" Valdes, a parking executive from Los Angeles, who is 1.78m, described his experience trying to use the bathroom on a recent American flight to Washington.

"If you are one inch taller, I don't know how you'd get in there," he said. "I saw some big guys [on the flight] and wondered . . ."

Travellers and consumer groups have bemoaned the downsizing of personal space on planes for years, watching as the average seat, once 45cm wide, shrank by 3.8cm, and the distance between rows went from an average of 89cm to 78cm - 71cm on some airlines.

But bathrooms? Really?

123RF On some of the newer planes flown by American, Delta and United airlines, the bathrooms in coach are just 61 cm wide.

"Given the trend line in the decreasing of personal space, this is just another instance of the airlines treating their customers as profit points, not as actual people," said John Breyault, a vice president of the National Consumers League. "I challenge any airline executive at any airline to have to change the diaper of a screaming infant in a two-foot-wide bathroom."

(Note: The tiny bathrooms are equipped with pull-down changing tables. But fitting an adult, a baby and a nappy bag in the space would require some manoeuvering.)

At 1.8m, Zach Guimond, a manufacturing engineer from Iowa has grown accustomed to being squeezed when he travels. But on a recent flight - he can't remember the model of plane - he found himself in a bathroom so tiny, he had to lean to one side to fit inside.

"Not only was there barely enough room to turn around, the ceiling was sloped, and I couldn't even stand up straight," he said. "It was pretty uncomfortable."

He pulled out his phone and scrolled to a selfie he had taken. His head is angled against one of the walls, a grimace on his face.

Shirley Sosin, a retiree from California, remembers the good old days of flying when "you could put our makeup on" in a plane bathroom. "Men could shave. Things have changed," she said.

123RF The new-style bathrooms free up enough space to fit six more passengers onboard.

MY, HOW THEY'VE CHANGED

But the reality is this: The nation's airspace can handle only so many flights per day, so airlines have done the next best thing - they have found ways to put more passengers on every flight. A few inches here and there can make a big difference to an airline's bottom line.

Gary Weissel, managing officer of Tronos Aviation Consulting, estimated that airlines like American could generate about US$400,000 (NZ$581,000) a year in additional revenue for each seat added. Weissel based his calculation on typical jet usage and the average fare.

Last fall, American told investors it could make an additional US$500 million in revenue through 2021 by revamping its 737-800 jets to fit 12 more passengers and its Airbus SE A321 planes to fit nine additional travelers.

According to SeatGuru.com, American's 737 MAX 8 has 172 seats - 12 more than the 737-800, which had 160. For those keeping track, that's two additional rows. United's 737-700 jets had 118 seats, but its newer 737-800V3 jets have 166. Translation: That is 48 more people competing for overhead storage.

It does not take an engineer to know that all that space for seats has to come from somewhere.

On its website, Rockwell Collins, the Iowa-based company that manufactures bathrooms for Boeing's 737, boasts that installing its Advanced Spacewell lavatories can free up space for six additional passengers.

All this downsizing comes as the average American's waistline is expanding.

According to the Centers for Disease Control and Prevention, the average American man weighs 196 pounds - nearly 30 pounds more than he did in the 1960s. The average American woman weighs 75 kilograms - nearly 9kg more than she did in the 1960s.

In addition, nearly 79 million Americans are obese - that is 35 per cent of the population, and the number is projected to reach 50 per cent by 2030.

But you do not have to be overweight to feel the squeeze when you fly.

123RF United's 737-700 jets had 118 seats, but its newer 737-800V3 jets have 166.

There is no federal standard for bathroom size on single-aisle aircraft, so the decision is largely left to the airlines and manufacturers. However, aircraft with 60 or more seats that do not have an accessible bathroom for people with disabilities must provide an onboard wheelchair to provide access as long they have been given 48 hours notice. The chairs are designed to help disabled passengers get to the bathroom door - but not necessarily inside the lavatory.

Alison McAfee, a spokeswoman for Airlines for America, which represents some of the nation's largest carriers, counters that airlines have invested billions to upgrade their fleets and give travellers - at every price point - more options.

Indeed, airlines brag that today's planes are lighter and more fuel-efficient, with roomier overhead bins and WiFi connections so speedy that travellers may forget they are hurtling through the air 30,000 feet above the ground. Though in many cases, passengers have to pay extra to connect or even to use the overhead bins.

"In 2017 alone, airlines invested an estimated US$19.9 billion to enhance their product and customer experience, including newer larger aircraft, larger overhead bins and various amenities that customers want when they travel," McAfee said.

SUPPLIED More passengers on board means more competition for overhead locker space, and that room has to come from somewhere.

But what about the tiny bathrooms?

"The idea that airlines would intentionally downgrade the flying experience or undermine safety is a flawed premise," she said.

On a United flight from Houston and Orlando, Zach Honig, editor-at-large for ThePointsGuy.com, a travel-advice website, watched passengers as they emerged from the smaller lavatories.

"All of them seemed really surprised," he said. Not just by the size, he said, but by the sink, which was so tiny it was impossible to emerge without getting soaked. The bathrooms, Honig later wrote on his blog, were "shockingly bad".

Maddie King, a spokeswoman for United, said lavatories on the airline's newer 737s are the "industry standard". Joshua Freed, spokesman for American Airlines, said the company is "not unique and not alone" in lavatory size. Delta Air Lines declined to say how many of its planes have been equipped with the smaller bathrooms, but they do include jets that fly out of National.

All said they are not aware of passenger complaints about the bathrooms. However, earlier this year, flight attendants from American Airlines raised safety concerns about the smaller bathrooms with chief executive Doug Parker.

"We certainly hear about it from passengers," said Jeffrey Ewing, national safety and security chair for the Association of Professional Flight Attendants, which represents American's flight attendants. "The bathrooms are very small. The sinks are tiny. They are not very comfortable."

123RF Flight attendants from American Airlines raised safety concerns about the smaller bathrooms with the chief executive.

Flight attendants from other unions have also raised concerns.

"These 'space-saving' bathrooms have created accessibility issues for passengers of size and passengers with disabilities," said Taylor Garland, spokeswoman for the Association of Flight Attendants-CWA.

"Depending on the airline's configuration, the aft bathroom doors have caused physical injuries to passengers and crew. We continue to press airlines to mitigate these issues and ensure accessibility for all passengers. But this issue deserves attention and needs to be addressed."

PRICE OVER COMFORT

So how much have bathrooms shrunk? Airlines won't comment on specific dimensions, and manufacturers such as Boeing said the information is proprietary.

A spokeswoman for Rockwell Collins, the Iowa-based company that manufactures lavatories for the Boeing 737, said they, too, are barred from commenting on bathroom dimensions but directed a reporter to the company's website, which details the benefits of the lavatory options offered.

Its Advanced Spacewell lavatory frees "up to seven additional inches [7cm] of cabin space". Airlines interested in installing the lavatories on existing aircraft could free up space for "an additional 6 passengers in certain configurations", the website notes.

The company indicated that the trend toward smaller lavatories is driven in part by the rise of low-cost carriers like Spirit and Allegiant that are catering to fliers who care more about price than comfort.

"As the industry continues its move toward a multitiered model of travel, so has the need for different lavatory options," said Pam Tvrdy-Cleary, a spokeswoman for Rockwell Collins.

Consumer groups, however, are fighting back. They argue that downsizing on planes - whether seats or bathrooms - isn't just a matter of comfort but also of safety.

The Flyers Rights Education Fund last year petitioned a federal appeals court to impose a moratorium that would stop airlines from reducing the size of seats. Judge Patricia Millett of the US Court of Appeals for the District of Columbia Circuit denied the request, but she did instruct the Federal Aviation Administration to explain why smaller seats are not a safety hazard.

The FAA responded over the summer saying it is up to the airlines to determine the appropriate seat size, noting the issue is one of comfort, not safety.

As part of the FAA reauthorisation legislation passed in September, lawmakers directed the FAA to issue regulations that establish standards for minimum seat size. Whether that will lead to more comfortable seating, however, is unclear. Paul Hudson, president of Flyers Rights, the group that filed the petition, is concerned that the FAA will only reiterate its earlier position.

The US Department of Transportation's inspector general, however, has launched an audit that will look at whether changes in seat design may have an impact on evacuation procedures. The audit comes at the request of Representative Peter DeFazio, who is likely to become the next chairman of the House Transportation Committee when Democrats take control of the chamber in January.

Weissel, the aviation consultant, said complaints about the bathrooms are unlikely to discourage airlines from trying to find new ways to add even more seats. There is too much revenue at stake.

Add to that this: The vast majority of the public flies so infrequently that people may not even realise the bathrooms have become smaller. Even if they do, they may not care, he said.

He may be right. Personal space may be shrinking, but the appetite for travel remains robust.

Airlines for America said it expects record numbers of people to travel this holiday season.

And officials with the Transportation Security Administration expect to screen more than 25 million passengers nationwide between now and November 26 - a 5 per cent increase over last year.

Breyault, of the National Consumers League, said he thinks the demand is tied to the economy rather than better service.

"We live in a big country, and people have to fly all the time because they don't really have a lot of great alternatives."

For some, upgraded wireless and roomier overhead bins may be enough. Honig said the WiFi on the flight was the best he has ever experienced, though he noted that it was not free. As for the bathroom, he figures there is only so much give. He is looking on the bright side.

After all, he said: "There's no way they can get any smaller unless they shrink the passenger."