I have 30 women with sewing machines in the same room. They all are using basically the same amps... 12 amps. How many breakers do I need and of what ratings?

OK, J Hudson

Lets think about this, each breaker can handle up to 20 Amps. Each line uses a 12 Amp Sewing Machine. 12 from 20 =8 Amps. On raw math alone, you can put one sewing machine on one circuit, safely.

Treating each sewing machine as a motor load, and making an assumption that this is an industrial setting, your sewing machines would be considered continuous loads. This brings the loads ampacity to 15A (125% of the motors load), so like donf states, the load is one sewing machine per breaker, with no additional load exceeding 5A being placed on that same breaker.

12 amps each? Are these large, industrial machines?

I would use 30 20 amp breakers. Lighting on separate circuit(s).