The standardization of motor sizes has the advantage that there are only a limited number of different flange dimensions and shaft diameters. NEMA stands for "National Electrical Manufacturers Association" and is an American standardization organization. The NEMA size of motors is used for stepper motors as well as for brushless DC motors. It is a useful abbreviation for the size of the motor in terms of power and torque. Frame size refers to the diameter of the motor face, or flange dimension, although the length may vary. The flange dimension in inches gives the name of the frame size: so Nema 17 means 1.7" and equals 43.18 mm. By conversions, the actual flange dimension is 42 mm. Partly the motors are adapted for the European market. Characteristic values for the various classes are shown as examples in the table below.
| size | Torque range [Nm] | Flange [in] | Bolt circle [in] | Bore [in] | Shaft diameter[in] |
| 8 | 0,01-0,04 | 0,8 | 0,4455 | 0,078 | 0,1575 |
| 11 | 0,06-0,12 | 1,1 | 0,6435 | 0,1 | 0,1965 |
| 14 | 0,05-0,5 | 1,4 | 0,8061 | 0,118 | 0,1965 |
| 17 | 0,2-1 | 1,7 | 0,8627 | 0,118 | 0,1965 |
| 23 | 0,5-3 | 2,3 | 1,3152 | 0,2 | 0,25 |
| 34 | 3-12 | 3,4 | 1,9374 | 0,22 | 0,375 |
| 42 | 12-20 | 4,2 | 3,75 | 0,25 | 0,375 |