Most generators are rated in watts. Volts x Amps. If you you have a 120 watt bulb at 120 volts you would have one amp. Motor circuits such as circulating motors for heat and compressors for refrigerators must be calculated differently. It takes about three times the current to start a motor.
Most motors have the amperage rating on the name tag.
If the motor has a nameplate rating of 3 amps you might want to add 9 amps on your generator calculations. Also because most generators may run over a period of time you may not want to run at full capacity.