Trapezoid Perimeter Calculator

P = a + b + c + d. Sum of two parallel sides + two non-parallel.

Inputs

Result

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How to use this calculator

  • Enter the two parallel side lengths (a, b).
  • Enter the two non-parallel sides (c, d).
  • Enter height for area calculation.

About this calculator

A trapezoid has exactly one pair of parallel sides (US definition; UK calls it "trapezium"). Perimeter is the sum of all four sides. Area = ยฝ(a + b)h where a and b are the parallel sides and h is the perpendicular height between them. Isosceles trapezoid (c = d) is symmetric โ€” common in pediments, drink-can profiles, and bridge spans.

Frequently asked

US vs. UK terminology?+
US: "trapezoid" = one pair parallel; "trapezium" = no parallel sides. UK: opposite. Conventions vary; this calculator uses US.
Why height for area but not perimeter?+
Perimeter is the sum of sides โ€” height isn't a side. Area depends on perpendicular height between parallel sides.
Can c and d differ wildly?+
Yes โ€” only need parallel sides for it to be a trapezoid. c, d can be any (positive) length subject to consistent geometry.
Isosceles vs. general?+
Isosceles: legs equal, line of symmetry. General: legs differ. Both are trapezoids.
Does parallelogram count?+
Inclusive definition: yes (two pairs of parallel sides). Exclusive: no (only one pair). Most US sources use exclusive.

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