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Trapezoid Side Calculator

Find the length of the missing side (a, b, c or d) of a trapezoid with the trapezoid side calculator.

For the perimeter. Leave at 0 to skip.
Clear
Area26
Median (midline)6.5the average of the parallel sides
Height4
Perimeterenter both legsthe legs are not fixed by area alone
Area as a rectangle26median × height gives the same answer

The formula

A = ½(a + b) × h

Area scales with the square

Double every length in a flat shape and the area quadruples; triple them and it grows ninefold. Perimeter, being a length, scales in step with the sides. That mismatch is why bigger shapes enclose proportionally more area per unit of edge — and why a circle, having no corners at all, encloses the most area for a given perimeter of any shape.

Units

Whatever unit you enter, the area comes out in that unit squared and the perimeter in the unit itself. The calculator is unit-agnostic — enter centimetres and read cm and cm², or feet and read ft and ft². Just do not mix units between fields.