Trapezoid Calculator

Base a

Base b

Height

Side c

Side d

Result

Area32
Midline8
Perimeterукажите боковые стороны
Base offset2
Height check4

Average the parallel sides, multiply by height

Area from the two parallel sides and the height, plus the midline, perimeter and the offset between the bases.

The area of a trapezoid is the average of the two parallel sides times the height. That average is also the midline, so the formula reads as "midline times height", which is far easier to remember.

The height is the perpendicular between the parallel sides, not the slanted side. Confusing them is the standard mistake: on any non-right trapezoid the slanted side is always longer than the height.

What this calculator shows

The area and the length of the midline
The perimeter, once both slanted sides are entered
The offset between the bases — half the difference in their lengths

What to keep in mind

The height must be perpendicular to the parallel sides; a slanted side will not do.
The formula is identical for right and isosceles trapezoids — the shape does not change the area rule.

FAQs

What is the midline?

The segment joining the midpoints of the slanted sides. It runs parallel to the bases and equals their average, which is why area is midline times height.

How do I find the height from the area?

Divide twice the area by the sum of the bases. That check is printed as its own line so the result can be verified.

What makes a trapezoid isosceles?

Equal slanted sides, equal base angles and equal diagonals. It does not change the area formula but makes finding the height from a side straightforward.

Can I get the area without the height?

There is a Heron-like formula using all four sides, but it is unwieldy. Finding the height from the right triangle cut off the end is usually quicker.

Worked example

Bases of 10 and 6

Input: Bases 10 and 6, height 4

Output: Area 32, midline 8

Note: The midline is 8, exactly the average of the bases. A rectangle 8 by 4 has the same area, which is a quick way to sanity-check the answer.

Useful links

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Trapezoid Calculator

Result

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