The official rules for the game of darts dictate a minimum throwing distance of 7 feet and 9 1/4 inches, measured horizontally from the board's face. An official throwing line, or toe line, is at least 18 inches long and must be clearly marked at the precise throwing distance.
Diagonally, the distance from the center of the bulls-eye to the back of the throwing line must measure 9 feet and 7 3/4 inches. In addition to an established minimum throwing distance, the height of the dart board off of the ground is regulated. The center of the bulls-eye must be exactly 5 feet and 8 inches high.
This distance, along with all other dart rules and regulations, is governed by the Professional Darts Corporation (PDC) and the British Darts Organization (BDO). The PDC and BDO operate under the World Darts Federation. The list of rules and regulations for darts is extensive, and there are, in fact, two sets of rules; the general playing rules and the tournament and championships playing rules.
Every aspect of the game is regulated. There are established rules for throwing the darts, scoring, dartboard type and size, and even lighting during the game. BDOdarts.com and thedra.co.uk list the entirety of the rules, requirements and regulations.