My new car has air conditioning, power windows, power locks - the whole nine yards.
Interestingly, this seems to be one of the most disputed phrase origins. Many possible explanations, yet no consensus on the true origin. Take your pick.
This phrase has also been attributed to WW2 fighter planes. Nine yards was the exact length of a belt of 50-caliber ammunition for the Corsair fighter. If a target was shot at with the entire band, it was said to have been given the whole nine yards.
Alternative: A tailor making a high quality suit uses more fabric. The best suits are made from nine yards of fabric.
This may seem like a lot but a proper suit does indeed take nine yards of fabric. This is because a good suit has all the fabric cut in the same direction with the warp, or long strands of thread, parallel with the vertical line of the suit. This causes a great amount of waste in suit making, but if you want to go the whole nine yards, you must pay for such waste.
The phrase certainly applies to the preparation of a full set of men's clothing. To fully understand this, you need to know what constituted a full set of clothing for a man in the 17th and 18th Centuries where the phrase can first be traced.
The items of clothing for a man were a Westkit (waistcoat), Breeches (pants) and a Great Coat. The material requirements to tailor these garments (even with a minimal amount of waste) is nine yards of material (45" width in the 1800s). A Westkit requires 1.5 yards, Breeches requires 2.0 yards and the Coat requires 5.5 yards for a total of 9.0 yards. These amounts can be confirmed with many museums, historians or period re-enactors.
The reason that the Coats required so much material was that they went from shoulder down to the back of the knee in length, and then the lower portion of the coat was full and pleated, almost like a dress. The pattern for the coat below the waist is almost a full circle
Alternative: The whole nine yards refers to the amount of fabric in a proper Scottish kilt. Nine yards of fabric seemed positively way too much for a skirt, The kilt, much like the suit, must have the fabric oriented in the proper direction. The plaid (or Tartan) has to be matched perfectly, so it doesn't look crooked. This alone takes a huge amount of cloth. The nine yards is the area of the fabric the tailor starts with, much of which ends up as scrap. Additionally, a kilt does not simply wrap around the waist. It also includes fabric that is worn up and over the shoulder. Old style kilts were used as blankets, toweling, or whatever else came to mind. There is a tale about one man using his to escape from a window of his lady-friend's bedchamber when her husband came home early.
Alternative: Old style concrete mixers, or coal bins, held nine yards.
Alternative: Many old sailing ships had three masts, the fore, main, and mizzen. Each mast held three square sails. The horizontal stays that support the square sails are called yards. Hence the ships had nine yards.
Depending on the sailing conditions, more or less sails would be raised. In the best conditions peak speed could be achieved by raising all nine main sails - the whole nine yards.