The length of a ramp relates to its height and the length of the ground beneath it. The three measurements form a triangle, with the straight ramp as the triangle's hypotenuse. According the Pythagorean theorem, the square of the ramp's length equals the sum of the squares of the two other sides of the triangle. This relationship also lets you calculate lengths that are more difficult to measure than ramps, and it has multiple mathematical and trigonometric applications.
Square the vertical distance from the ramp's highest point to the ground. If, for instance, this point is 6 feet high, then 6 ^ 2 = 36.
Square the horizontal distance from one of the ramp's end to the other. If this distance is, for instance, 24 feet, then 24 ^ 2 = 576.
Add together the two squared values: 36 + 576 = 612.
Find the square root of this sum: 612 ^ 0.5 = 24.73 = approximately 24 feet 9 inches. This is the ramp's length.