746 Watts is 1 HP...or in your case 4100 watts..
P/E= about 18 amps..
BUT this is in a perfect world..That would assume the compressor was steady and not cycling (High / low Rotor load) and Does not account for startup rotor load...nor does it assume, line loss or switch gear loss..
30 Amp 8 awg for a short distance would be fine..
As was said before if the house and garage isn't too far, and you have a slot for the breaker, you can get some 1 inch conduit, Ell's, 90' Condulets, whatever is needed..rent a bender, and install a permanent location yourself without too much trouble.