The whole nine yards

Several origins of the phrase "the whole nine yards" have been suggested, such as the amount of fabric needed to make some particular garment. None of the explanations has any real evidence for it.

from the alt.folklore.urban FAQ:

True. There is no good etymology for the phrase "The whole nine yards."
True. Suggestions have included: Volume in a concrete mixer, coal truck, or a wealthy person's grave; amount of cloth in a man's custom-made (i.e., "bespoke") suit, sports games, funeral shroud, kilt, in a bolt of cloth, square area in a ship's sails, and volume in a soldier's pack.

9 yards = 324 inches
9 yards != 100% effort
9 yards != a first down

Well, take your pick. This word seems to have no clear origin, though lots of people will feed you assorted bullshit . The following discussion about the origin I found at The Phrase Finder website (www.shu.ac.uk) and it seems to to a pretty good job of giving the whole... Okay, I stopped myself. Take your choice.

1. It comes from the nine cubic yards capacity of US concrete trucks and dates from around 1970s. I know from personal experience of working on the Spaghetti Junction construction site in the UK that trucks often 'lost' part of their load between the mixing depot and the proper destination. The many concrete forecourts in the West Midlands area bear continuing witness to that. A full load delivered to the roadworks was a rarity and was usually commented on, so a phrase being coined to mark the event seems believable - not in the UK though as concrete trucks here at the time carried seven cubic yards.
2. The explanation refers to World War II aircraft, which if proved correct would pre-date the concrete truck version. There are several aircraft related sources, 1. the length of US bombers bomb racks, 2. the length of RAF Spitfire's machine gun bullet belts, 3. the length of ammunition belts in ground based anti-aircraft turrets, etc. It is worth mentioning that Charles Browning, of the family that manufactured armaments for the US forces has said that they never made any machine gun belts that were nine yards long.
3. Tailors use nine yards of material for top quality suits. Related to 'dressed to the nines'? Again, this conflicts with circumstantial evidence as tailors I have been in correspondence with say no suit would require so much material.
4. The derivation has even been suggested as being naval and that the yards are shipyards rather than measures of area or volume.
5. Another naval version is that the yards are yardarms. Large sailing ships had three masts, each with three yardarms. The theory goes that ships in battle can continue changing direction as new sails are unfurled. Only when the last sail, on the ninth yardarm, is used do the enemy know which direction the ship is finally headed.

To illuminate reason number three above:

While no garment would require nine yards of fabric, a seamstress friend of mine tells me that in the glory days of tailoring it would sometimes be appropriate to use that much.

To make a suit of the most exceptional quality, one would want precisely align the grain of the fabric of each small component of the suit (i.e. the sleeves, the collar, etc.) This would require that vast amounts of fabric go wasted, so that in order to make a complete suit, one would need a total of nine yards of fabric.

It is common tradition throughout the world's militaries to celebrate when someone is promoted. When a Young Officer is promoted, right before they leave Britannia Royal Naval College in Dartmouth, it is tradition to visit nine pubs throughout Devon and drink a glass of beer or ale about two inches wide and a foot tall. Participants drink three of these per pub, hence "the whole nine yards".

The nine establishments hit are not important- almost all the pubs I visited in Devon while crossdecked at BRNC had the requisite glasses for the tradition. In fact, after about the third pub, you can't remember anything anyhow. This would be a problem, considering the tradition is largely an oral tradition, if the pubs or the order of the pubs were important. In fact, the requirement to drink three glasses per pub is loose too. Serving as the designated driver for the raucous little caravan, I noticed people were losing the ability to count to three, and instead just left for the next pub when they felt ready.

Of historical note, "the whole nine yards" actually predates the World War II explanation above. My hosts explained this tradition actually predates the college (which was founded in 1905), and probably predates the establishment of naval facilities at Dartmouth (in 1863) because the tradition is observed throughout the Royal Navy.