How Many Amps Does a Bench Grinder Use. To figure out how many amps your bench grinder uses at one time, you need to divide watts by volts. So if you have a 250-watt bench grinder, and it uses 110 volts, then the bench grinder is using. The answer to that problem is the 250-watt bench grinder will use just over 2 amps. Don't think about HP.