What is the origin of "the whole nine yards"?

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Why: Norma said it last night at dinner. She is just full of idioms.

Answer: Nobody knows! In lieu of an answer, here are a bunch of unlikely/debunked theories:

• A square-rigged sailing ship had 3 masts with 3 "yards," or horizontal poles that held up the sails. 3x3=9 yards.
• In WWII, a length of ammunition for a machine gun was 9 yards long.
  
• Coal trucks in New England originally had 3 sections that each held 3 cubic yards of coal.
• Ready-mix concrete trucks hold 9 cubic yards when fully loaded.
• It takes exactly 9 square yards of material to make a man's 3-piece suit.
• It took 9 yards of material to make a dress for a colonial lady.
  
• Brides in the olden days had veils that were 9 yards long.
• An undertaker used 9 yards of material to make a funeral shroud.
• A dead rich person could afford to have 9 yards of dirt removed for his grave, while a dead pauper couldn't have such a large plot.
• It was a sarcastic description about a football player's failure to reach the 10th yard.
  

Source: The Straight Dope

The More You Know: The earliest known instances of the phrase in print are both from 1962. One was in a short story in the literary magazine Michigan's Voices, and the other was in a letter in the magazine Car Life.