Feed wire sizing to my garage

For your small simple single phase system fed from 240 V - a quick way to figure out what you need -
Sum the kW ratings of all the equipment you think you will be running at the same time, and add a 50% load growth margin.
Then divide that number by 240 V to determine conductor ampacity (size).
So lets say you sum up the kW rating of all your simultaneous equipment to be 5 kW, for example. Plus 50% makes that 7.5 kW, and 7.5 kW/240 = 31.25 amperes. If you are using UF-B, you can use No. 8 protected by a 40 A 2-pole breaker Despite what the code permits, I never like to run UF without some protection, and I frequently use either liqua-tite flexible conduit, or PVC conduit.

If you doubled up No.4, then you have plenty of capacity and the doubling up of conductors may not be an issue for your jurisdiction. It will depend on what edition (and sections) of the NEC your jurisdiction adopts -- if any. Additionally, such a practice is permitted in many other venues and is an accepted and safe practice if basic rules are followed - which is likely the case in your circumstance of being installed by a licensed electrician.

Good luck
 
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