Free · Algebra and geometric models

Trapezoid Area and Boundary Length

Find trapezoid area, perimeter and leg-height angle relations.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

For the worked inputs, Area = 20.

A=(a+b)h/2; P=a+b+c+d

Worked example

Enter these known values and leave the other values blank.

a (base)
8 cm
b (base)
2 cm
h (height)
4 cm
Area
20 cm²

Assumptions and limitations

  • Parallel base lengths and perpendicular height are positive.
  • Two arbitrary legs plus a height must permit a consistent trapezoid; area alone does not determine the legs.
  • A leg equal to height is perpendicular to the bases. Legs may not be shorter than height.

Common questions

What must I enter?

Choose the mode when available and enter its independent known quantities. Leave an unknown editable quantity empty to use a supported inverse.

How should I use the result?

Interpret the numbers within the stated mathematical assumptions. Available unit selectors convert quantities; display rounding does not replace the internal calculation.

References

Explicit real-model bounds validate dimensions, inverse branches and discrete controls omitted or approximated in this capture. Perpendicular-leg equality is valid, so the captured strict leg-height bounds include equality. The international acre is exactly 43560 square international feet; Bookify replaces the rounded captured area factor.

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