why are coins round?

Coins are made from dies that punch holes in coins. In order to make the dies, they are machined down on a lathe. A lathe basically spins and a cutter shaves away the material. Since it spins, the die perfectly round and that is why the coins come out round.

In case you really are curious, money comes in all sorts of shapes and sizes, although almost everything you will see in the USA is round coins and rectangular paper money. There was an interesting display at the last American Numismatic Association show in San Francisco that had 3,4,5,6,7,8,9,10,11,12, etc sided coins from all over the world with most values up to 24 and a few higher. Technically the reeded edges on most coins make them not round, but over 100 sided (with a variety of reeding options.)

There is a lot of odd and curious money out there like cross money from Katanga, Swedish plate money, and large stones from Yap. Early American money (wampum) was beads and blocks of tea also circulated in the American colonies as money. I have actually barely touch the tip of the iceberg here and there is a lot more information on-line, if you care to look it up, all the way back to Chinese cowrys 3000 years ago, but you are probably bored with this diatribe by now.

It is true that most coins are round although I have seen plenty in other shapes, including square. I think that the answer probably lies in the technology of the earliest minters - whose output was also round(ish). A die was hammered onto a thin sheet of metal. Perhaps a circle was easier to reproduce than some other shape. In any event, once the fashion had been established, it stuck - as is the case with so many other objects passed down to us.

All coins are not round. Before introduction of decimal currency in India, we had half anna and two anna coins that were square in shape.I have them in my collection.

They;re not!!!! Have you ever seen a twenty or fifty pence piece in the UK? They are heptagons......7-sided!!

PLUS.... if they weren't round, we wouldn't have 'em to spend, silly-billy!!! ;-)

Easier to roll.

So they fit in Vending machines??

They were made round to facilitate SLOT Machines.

if they were square they would poke holes in your pocket

That's a STUPID question!