What do the numbers mean on a brushless DC motor?

Brushless DC (BLDC) motors can have a range of numbers on them:

What do they mean?

• A four-digit number (e.g. 2212)

This number describes the dimensions of the stator inside the motor. The first two digits are the diameter (in mm) and the second two digits are the height (again, in mm.)

Kv - or Kv - has some really good answers at the provided link so I won't go into detail here, but it is approximately the RPM per volt.

• A number with N and P (e.g 12N14P)

This describes the magnets present. The number before N is the number of electromagnets and the number before P is the number of permanent magnets. More magnets means more torque, but also higher cost and size.

• I believe your first point is wrong. Those numbers measure the stator size, not the motor size.
– ifconfig
May 31, 2020 at 16:09
• I think you're right; I knew they were dimensions so quickly Googled to check which way round and it seems the first few links make the same mistake - but searching for mechanical drawings clearly show the rotor is wider than the motor numbers. Answer updated. May 31, 2020 at 16:41
• The size numbers did originally refer to the stator (and generally still do for FPV quads, as 2204 was the original CDROM motor), but various Chinese makes have switched to use the overall motor size - presumably to make their motors sound bigger when ordering on-line. You need to actually check the dimensional diagram to see which scheme a particular motor is using. Here's an example that uses the overall size: oscarliang.com/1811-micro-brushless-outrunner-motor-review Jun 1, 2020 at 8:33