Australians lose 255 million coins every year - down the back of the couch, taken overseas in the pockets of tourists and stuck to footpaths.

The Royal Australian Mint's chief executive, Ross MacDiarmid, told bemused senators in an estimates hearing on Tuesday night that it costs $110 million annually to replace these coins.

The five cent coin actually costs six cents to produce. Credit:Danielle Smith

"Mostly coins we provide are against coins that disappear down the back of chairs, down the back of car seats, into rubbish dumps and, in some cases, taken overseas," he said.

"That is the most interesting thing I've heard all day," exclaimed Labor senator Sam Dastyari.