Ok, no laughing. Doing up my first swatch for my first piece of clothing. How big do you need to make the swatch??? 
[size=2][color=blue]The Mod Squad was here[/color][/size] 
I think they say usually 4 inch square. I however am really bad and only do enought to put my little guage thingy up to it! :oops:
A 4" square is a decent size. But I usually determine my swatch size depending on the gauge. For example, this yarn’s gauge is 4 sts = 1” #8 needles (assume stockinette). So I would cast on 14 sts and work stockinette over 4 sts with a 5 st knit border on each side. The border pops out the stockinette and makes it easier to measure. Just one humble person’s technique… 