Patrons of the footlong sandwich of U.S. food chain Subway are reeking mad over the alleged advertising fallacy of its footlong sandwich which was discovered to be lacking an inch short.

The uproar started when Australian Matt Corby took a fancy of taking a photo of his sandwich on Thursday last week, complete with an attached tape measure, to prove the footlong was not really a footlong after all. Posting his discovery on Subway's Facebook fanpage, it immediately collected hundreds of thousands of likes and subsequently, a huge collection of comments, plus shared over 3,700 times.

But Subway Australia said the footlong label was just a description.

"The 'Subway Footlong' was a registered trademark as a descriptive name for the sub sold in Subway restaurants and not intended to be a measurement of length," it said.

Its explanation, which observers found already lacked appeal, all the more got doused when the company put the blame on its sandwich suppliers.

"Looking at the photo doing the rounds, showing a slightly undersized sub, this bread clearly is not baked to our standards,'' the company said.

It would have been better if Subway owed up to the sizing discrepancy, according to Dr Paul Harrison, Chair of Consumer Behaviour at Deakin University.

"That's the problem with these trademark names, if you use a name like footlong which is in common usage, you're creating real problems for yourself," portal www.3aw.com.au quoted Mr Harrison as saying.

"Subway should be saying sorry, we mucked up and next time we'll do better than a footlong," he added.

Subway is the world's largest fast food chain with 37,000 locations across the globe.

"People look for the gap between what companies say and what they give, and when they find the gap - be it a mile or an inch - they can now raise a flag and say, 'Hey look at this,' I caught you," Allen Adamson, managing director of branding firm Landor Associates in New York, said.