I have a 100 amp panel in the house and I have to run 30 feet to my garage and I need a 20 amp for the compressor one 20 amp for a welder and a 15 amp for lights and a 20 amp for 8 recpeticals I do have #4 aluminum will this work for a 50 amp sub panel or what size sub do I need to have

Are the compressor and welder 220v? If so your exceeding the limit by about 7 amps. The 2 20 amp 220v sockets would take 40 of the amps your sending there. That leaves 10 amp 220 or 20 amp 110. You need to either share a plug between compressor and welder or set sites a little lower.

Are the compressor and welder 220v? If so your exceeding the limit by about 7 amps. The 2 20 amp 220v sockets would take 40 of the amps your sending there. That leaves 10 amp 220 or 20 amp 110. You need to either share a plug between compressor and welder or set sites a little lower.
Can you explain this a bit? Your logic here is not really accurate.

You do not add up the circuits. What "limit" is being exceeded?

Two 20A circuits does NOT "take up" 40 amps.