Add up the appliances on a circuit or panel, get the total load in watts and amps, and see the right breaker size for a 120V or 240V circuit.
Watts = volts x amps. Sum your devices, then divide by voltage for total current.
Continuous loads get sized at 125% so breakers don't nuisance-trip.
Get the next standard breaker up plus the minimum copper wire size to go with it.
All calculations run locally in your browser.
Stay safe, stay sized.