Free · Algebra and geometric models

Isosceles Trapezoid Area, Diagonal and Perimeter

Calculate measures of a trapezoid with equal legs from its parallel bases and perpendicular height.

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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.

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Formula and method

For the worked inputs, Area = 20, Leg (c) = 5, Perimeter = 20.

A=(a+b)h/2; leg²=h²+((a−b)/2)²

Worked example

Enter these known values and leave the other values blank.

Longer base (a)
8 cm
Shorter base (b)
2 cm
Height (h)
4 cm
Leg (c)
5 cm
Diagonal (d)
6.403 cm
Acute angle (α)
53.13 deg
Obtuse angle (β)
126.87 deg
Area
20 cm²

Assumptions and limitations

  • The bases are positive with long base greater than the short base.
  • Equal legs create two congruent right triangles at the base edges. Angle inverses use the acute lower-base angle.

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. The international acre is exactly 43560 square international feet; Bookify replaces the rounded captured area factor.

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