Quote Originally Posted by Woodsheal View Post
Actually, not 6 ells of double tartan, but 6 ells of tartan doubled, for a total length of 3 ells, or about 3-3.5 yards total length - depending on whether you're talking about Scottish (37") or English (45") ells! This was the size plaid issued to Highland enlisted troops in the British army. Civilian plaids could be a bit more generous, but usually no more than 5 yards.

Remember, the tartan fabric came off the hand looms about 27" wide, so two lengths had to be joined together lengthwise to make the completed plaid, with an approx. 54" width. So, 6 ells of tartan yields a 3 ells in length plaid.
That certainly makes more sense! Interestingly, three different sources mention the 5x18 foot size-- obviously somebody back then didn't do their A Levels in math!