Enter two parallel bases and height to calculate trapezoid area; add leg lengths for perimeter.
Cross-check area, perimeter, midsegment, horizontal leg offsets and isosceles diagonal evidence.
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Keep linear inputs in a consistent unit, verify that side lengths or coordinate points can form the stated shape, and treat sketches as explanatory unless explicitly marked to scale. Coordinate formulas can become unstable for nearly degenerate shapes, so invalid or nearly collinear inputs are rejected rather than silently returning misleading values.
For a trapezoid, area uses the lengths of the parallel bases and the perpendicular height: A = (a + b)h / 2. Using a slanted leg as the height can produce a plausible number that is geometrically wrong.
The shortest distance between the parallel lines is the height. If the input comes from a drawing with a sloping side, derive the perpendicular height from coordinates, an angle or a right triangle before calculating area.
Area can be known from the bases and height without knowing the leg lengths, but perimeter cannot. Do not infer missing legs from area alone unless additional geometric information makes the trapezoid unique.
If the two bases are equal, the area formula reduces to base × height, matching a parallelogram. If one base approaches zero, the formula approaches the familiar triangle area. These limits are useful quick checks on an entered formula or result.
If all lengths are in centimeters, the perimeter is in centimeters but area is in square centimeters. Convert all lengths to one unit before applying formulas when the source measurements use a mixture of units.
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