Trapezoid area calculator
Fill in what you know and leave the unknown box empty — it works out whichever one is missing. Nothing is uploaded; the arithmetic happens in your browser.
The formula
A = ½(a + b)h
Where this usually goes wrong
a and b are the two parallel sides. h is the perpendicular gap between them.
Worked example
Parallel sides of 8 and 12, height 5, gives 50.
Those numbers are already in the boxes above — press Work it out to see it, then change them for your own.
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