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Perimeter of triangles and quadrilaterals worksheets

A rectangle's perimeter can be found without really looking at the figure. A scalene triangle's cannot. These free printable worksheets put four sides on the page and ask a child to find and add all of them.

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Perimeter of triangles and quadrilaterals
Perimeter of triangles and quadrilaterals worksheet — Sides to 35 cm, free printable with answer key

The answer key prints on a separate page.

What's on this sheet

Every edge carries its own number, including the slanted ones. That is the opposite of the area sheets, where slant sides are deliberately left unlabeled so a child cannot mistake one for the height — here every side counts toward the answer, so a figure with an unlabeled edge would be unanswerable rather than harder.

Why this sheet works

The shapes are built from their side lengths rather than sketched, which means a triangle with sides 14, 13, and 17 is drawn as exactly that triangle. Two sheets with different numbers can never come out as the same picture, and a child checking their answer against the drawing is doing something the drawing supports.

How this one works

Perimeter of a 15 by 5 rectangle

sides:155155
sides:155155
sides:155155
15 + 5 + 15 + 5=40 cm
  1. Perimeter is the distance round the OUTSIDE — the length of the fence, not the size of the field. That is the whole difference between this and area, and it is where the usual wrong answer comes from.
  2. So there is nothing to work out — just walk round the edge and add: 15 + 5 + 15 + 5.
  3. 15 + 5 + 15 + 5 = 40 cm. Note the unit: cm, not square cm — a fence is a length, and a length never gets squared.

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