Gauge for socks

When doing a gauge for socks, do you swatch in the round or can you do the swatch flat?

I was wondering if it makes a difference, because flat you would be purling whereas you don’t purl in the round.

thanks

An in the round gauge swatch is best for any in the round knitting. Gauge is generally different, probably tighter, in the round. However, I don’t swatch for socks, I do them toe-up knit-to-fit and use whichever needles work best with my yarn.