Trapezoid Area Calculator
Enter the two parallel sides and the perpendicular height of a trapezoid to get its area from the formula (a + b) / 2 times height. Tick the perimeter option to add the two slanted sides and see the full distance around the shape too. Sides 6 and 10 with a height of 4, for instance, give an area of 32.
How to find the area of a trapezoid
- Type the first parallel side into the 'Parallel side a' field.
- Type the second parallel side into the 'Parallel side b' field.
- Enter the perpendicular distance between them in the 'Height' field.
- Read the Area card that appears below the inputs.
- To also get the perimeter, tick 'Also compute perimeter' and enter the slanted sides c and d.
- Use 'Copy result' to copy the area, and the perimeter when shown.
Examples
Parallel sides 6 and 10, height 4
a = 6, b = 10, height = 4
Area = 32
Decimal sides
a = 3.5, b = 6.5, height = 4
Area = 20
Perimeter from four sides
a = 6, b = 10, slanted c = 5, slanted d = 7
Perimeter = 28
Frequently asked questions
What is the formula for the area of a trapezoid?
Add the two parallel sides, divide by two, then multiply by the height. That is the average of the parallel sides times the perpendicular distance between them, so 6 and 10 with height 4 give 8 times 4, which is 32.
Which sides are the parallel ones?
A trapezoid has exactly one pair of parallel sides, often called the bases. Enter those two as a and b, and use the perpendicular height between them, not a slanted side, for the area.
Can I enter decimals?
Yes. Every field accepts decimal values in steps of 0.1, so 3.5 and 6.5 with height 4 return an area of 20. Results are rounded to six decimal places.
Do the numbers have to be positive?
Yes. Each side and the height must be greater than zero, since a zero or negative length is not a real trapezoid. The tool shows a short message instead of a result if a value is not valid.
How do I find the perimeter?
Tick 'Also compute perimeter' and enter the two slanted sides c and d. The tool then adds all four sides, so 6, 10, 5 and 7 total a perimeter of 28.
Is a trapezoid the same as a trapezium?
In British English a trapezium is the shape with one pair of parallel sides. The area and perimeter formulas, and this calculator, work the same under either name.
Does it matter if the trapezoid is right or isosceles?
No. The area only depends on the two parallel sides and the perpendicular height, so right, isosceles and scalene trapezoids all use the same calculation.
What units does this use?
It is unit free. Enter the sides and height in the same unit, and the area comes out in the matching square units, for example square centimetres or square inches.
Is anything sent to a server?
No. The area and perimeter are computed entirely in your browser, so the measurements you type are never uploaded or stored.
Learn more
- The trapezoid area formula and how to use it
Why the trapezoid area formula averages the parallel sides, how to find the perpendicular height, and how area differs from perimeter.
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