Parsec/Legends

"It's the ship that made the Kessel Run in less than twelve parsecs."

- Han Solo, referring to the Millennium Falcon

A parsec was a unit of distance equal to 3.258 light years. The system used by starship navigators throughout the galaxy to record the location of star systems was based on parsecs, with one unit on the coordinate scale corresponding to 15 parsecs.

Behind the scenes
By real world definition, a parsec is 360×60×60/2π Astronomical Units (AU). It is a measurement of distance based on apparent stellar motion as observed from Earth.

Since the Galactic Standard "AU", would be based on Coruscant's orbit (368 days) it would equal 150,349,907,726 meters. This makes a Galactic Standard parsec equal 31,011,894,586,294,500 meters. This is equivalent to 19,247,170,866,776.515 miles.
 * Note, that it is also possible that the Coruscant Day, Hour, etc. are 0.75% shorter than Earth's, in which case, the AU and parsec would be the same length as Earth's.

Earth has a year 365.2424 days long and an AU of 149,597,870,691 meters. This makes an Earth based parsec equal 30,856,775,813,057,300 meters. this is also equal to about 19,173,511,580,000 miles.

The "Decoded" version of the Star Wars: The Clone Wars episode Dooku Captured says that six parsecs equals about 114 trillion miles, although it would be closer to 116 trillion miles using either figure. Coruscant may be closer or farther to its sun than Earth is.

The Essential Atlas says a parsec is 3.26 light-years.

A New Hope Mess-up?
In Star Wars Episode IV: A New Hope, a boastful Han Solo claims that his spaceship made the Kessel Run in less than twelve parsecs. This is odd because he says parsec like it is a unit of time, but it really is a unit of distance.

However, one thing to keep in mind about Solo's claim of doing the Kessel Run in less than 12 parsecs is that the Kessel Run is through the Maw. Event Horizons around black holes are dependent on the speed at which you are traveling. A standard ship has to do the run in 18 parsecs because to cut the route any closer, the ship would get sucked in. The Falcon, however, is fast enough to straighten the route and cut over 6 parsecs off the distance traveled. This makes sense, since the Falcon is faster than most ships and he was using more power than what the engines should have been able to use. While this argument may all be after-the-fact justification for an actual scriptwriting error, the logic does hold, although Solo could have just been boasting to his potential clients.

On the other hand, a parsec is a very small unit in astronomical terms, only 3.26 light years. Elementary arithmetic shows that if the Galaxy is the same size as the Milky Way, roughly 30,000 parsecs across, any ship capable of traveling across the galaxy in only a few weeks would travel six parsecs in less than ten minutes-- hardly a significant difference. A similar issue arises in The Courtship of Princess Leia, when it takes more than a week to travel a distance of only seventy parsecs (the stated distance between Dathomir and Coruscant).

In the director commentary on the Blu-Ray Star Wars set it is explained that hyperspace travel requires heavy computation to compute a path that does not cause you to fly through a star and die. The Millennium Falcon has customized computation engines that allows to calculate shorter hyperspace paths more quickly than other ships. Shorter distances mean faster travel times. The ship reduces travel times by combination of being faster in a traditional sense, and by using more accurate navigation calculations.