Geometry
Leg of an isosceles trapezoid
The horizontal offset of each leg is half the difference between the bases. The leg is the hypotenuse of a right triangle with that offset and the height.
The Formula
leg = sqrt(h^2 + ((b - a) / 2)^2)
The horizontal offset of each leg is half the difference between the bases. The leg is the hypotenuse of a right triangle with that offset and the height.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| leg | Leg length | linear units | The slanted side of a symmetric trapezoid. |
| h | Height | linear units | Perpendicular distance between the bases. |
| a | First parallel side | linear units | The shorter base, usually. |
| b | Second parallel side | linear units | The longer base, usually. |
What Each Symbol Means
leglinear units
Leg length
The slanted side of a symmetric trapezoid.
hlinear units
Height
Perpendicular distance between the bases.
alinear units
First parallel side
The shorter base, usually.
blinear units
Second parallel side
The longer base, usually.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate the area of a trapezoid page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate The Area Of A Trapezoid, filed under Math. Every number the guide produces comes from substituting into this one line.