How this calculator works
The perimeter is the sum of both bases and both legs. Four-side mode also checks that the leg lengths can span the base difference with positive height. This is stricter than merely checking whether four segments close any quadrilateral. In angle mode each leg is a right-triangle hypotenuse, so dividing height by sine gives its length. The two signed horizontal projections must add to the difference between the bases. Measurements that fail this closure check are rejected.
Formula
P = a+b+c+d. From height h: c = h/sin A; d = h/sin B. Closure requires a-b = h cot A + h cot B.
Worked example
For bases 10 m and 4 m, height 3 m and two 45° base angles, each horizontal projection is 3 m and each leg is 3√2 m. Perimeter is 14 + 6√2, approximately 22.4853 m.
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Frequently asked questions
Why enter both angles?
A general trapezoid can have unequal legs. Two base angles fix both leg lengths; the bases then provide an independent closure check.
May one leg lean outwards?
Yes. An obtuse base angle gives a negative projection. The other leg must compensate so that the signed projections still equal the positive base difference.
Why reject equal bases in four-side mode?
Equal bases produce a parallelogram. Side lengths alone do not fix its height, so use a parallelogram tool for that case.