Gentlemen, please!

A day plaid that is two yards (or two metres or whatever you like) just hangs over the shoulder like Jock describes his. Unless you are really small in stature, you wouldn't be able to wrap it around your chest as shown in the old illustrations. You would need at least three or four yards for that. Those men are wearing it a bit like a piper's plaid, except looser fitting and definitely not pleated lengthwise. It wouldn't surprise me if some of them were made from single width cloth (27"-29").

Day Plaids, Laird's Plaids, or Shepherd's Plaids don't really seem to have an "official" length save that they appear to fall within the range of 2-4 yards.