What is the proper abbreviation for 1 million dollars?

Answer 1

There is no universal standard, but there are common ones:

• The most common abbreviation is a pseudo-metric abbreviation, where the "M" in $1M (or $5M or $10M) stands for million. This follows the use of "K" (kilo) as an abbreviation for thousands.
• The standard financial abbreviation for million is MM, e.g. $300 MM. This is a pseudo-Roman numeral abbreviation. Using this format, $1M represents $1,000 and $1MM is $1,000,000.

Of course, the actual Roman numeral "M" stands for 1000 and the "MM" represents 2000, not 1 million. The correct representation for 1,000,000 in Roman numerals would be an M with a horizontal line drawn above it. The horizontal line indicated the numeral was to be multiplied by 1000.