The first story I found had to do with WWII fighter pilots. I guess their ammunition belts had 9 yards of rounds for their machine guns. Upon engaging the enemy, once they’d spent all 9 yards of ammunition, they’d given it all they had, and it was time to reload or return home.
Another story involves Scotsmen’s kilts. Now the kilt is a pretty versatile piece of equipment. It works as clothing, a bedroll if you like sleeping in the buck and it’s excellent for dancing. Also, if you’re wearing one, you get to where kilt hose, socks and the sporran, a man purse.
Due to the pleats, or bunching, on a kilt, it takes about 6 to 8 yards of fabric to make one correctly. So when Scots, looking for fabric for their kilts, spoke to a wool merchant, they would ask for the whole 9 yards of material.
As always, thanks for reading!