Area of a Trapezoid Calculator

A = ½ × (parallel side a + parallel side b) × height.

Inputs

Result

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How to use this calculator

  • Enter the two parallel sides and the perpendicular height between them.
  • Read the area.

About this calculator

A trapezoid (US) or trapezium (UK) has exactly one pair of parallel sides. Its area is the average of the parallel sides times the perpendicular distance between them. Equivalent to a rectangle whose width equals the average of the two parallels.

Frequently asked

Why is it the average of the parallel sides?+
Cut the trapezoid horizontally at the midpoint and rotate the top piece — you get a rectangle whose width is the average. Same area.
What is the height in this formula?+
The perpendicular distance between the two parallel sides — not the slant length.
Does the formula work for an isosceles trapezoid only?+
No — works for any trapezoid (parallels need not be the same length, and the legs can differ).
How is a trapezoid different from a parallelogram?+
A parallelogram has two pairs of parallel sides; a trapezoid has only one pair (in the exclusive US definition).
Can I use this for a triangle?+
A triangle can be viewed as a trapezoid with one parallel side = 0. Plug in: A = ½ × (0 + b) × h = ½bh — the standard triangle formula.

Related calculators

Area of a Triangle Calculator
Three formulas: base × height ÷ 2, SAS (two sides and angle), and Heron's (three sides).
Area of a Parallelogram Calculator
A = base × height (perpendicular height).
Area of a Rectangle Calculator
A = length × width.
Area of a Rhombus Calculator
A = (d₁ × d₂) / 2 — half the product of the diagonals.
Trapezoid Perimeter Calculator
P = a + b + c + d. Sum of two parallel sides + two non-parallel.
Pyramid Volume Calculator
V = (1/3) × base area × height. For square / rectangular / triangular bases.

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