What is the official rule in Darts for space between the floor and the Bulls eye?

Answer 1

5' 8" from the floor (****where you are standing) straight upwards to the center of the cork (bullseye)
Use the third measurement of the triangle, 9' 7 3/8" from the center of the cork (from the face of the board) to the front of the toe-line on the floor.
(The 2nd measurement being 7' 9 1/4" from face of board to the front of toe-line (level w/ the floor/ horizontal distance from line to the board.)

**** Floors warp so if you measure from the floor area below the board on the wall, and the toe-line is lower due to normal settling of buildings your board will be too high.