Welder needs a 50 amp circuit.
That's the figure in the 90° column.Welder needs a 50 amp circuit. Just checked an ampacity chart and it say #8 THHN is 55 amps.
What welder?
Yes, you probably need the number 8. Some of the 250 wire feeders are really powerful and will output 300A. Miller 251, 252, the new 255. They have 60%duty cycle at their rated output. They rarely get run that hard in home shops.