[cabalamat]

> Pretty standard/common practice.

It's a common practise, but it's not a standard AFAIK. It's from latin mille which means 1000, so M=1000, and MM=1000000.

Unfortunately there is also a much more widely used international standard where k=1000 and M=1000000, so the M/MM forms are to say the least, confusing, and ought to be scrapped.

[swombat]

On the other hand, I've never seen anyone use 10M to mean 10k, so there doesn't seem to be any actual confusion caused by this.

1000 = k

1000000 = either m or M or MM

[rmc]

It's a common practise

That's the definition of a standard in the English language.

but it's not a standard AFAIK

There are no English Language standardisation bodies.