Big Sean -- Don't Be Deceived ... By the Size of My Yeezys

Big Sean is adamant ... he's NOT a size 8 when it comes to shoes -- and says there's a perfectly good explanation why he's been painted as a man with tiny feet.

FYI -- Kim Kardashian recently posted a pic showing the superstars who got first dibs on Kanye's new Yeezy shoes ... and the pic showed the shoe sizes on the corresponding boxes.

Jay Z and Diddy rock a size 9 ... and Big Sean got himself a size 8 ... underwhelming to say the least.

But Big Sean says you can't judge a man by the size of his Yeezys ... and he's got some hard evidence to back his claim.

Also, in case you were wondering why they call him Big Sean ... just check the Internet.