Maths · Area & Perimeter
Area Unfolder
This L-shape is awkward. Cut it into two rectangles you CAN measure.
Free to use and free to share. There is no sign-up, no score, and nothing a child does here is recorded or sent anywhere. What you may do with it, in full.
Loading the interactive exercise. Nothing you do here is saved or scored.
Why this works
A compound shape has no area formula of its own, so you make one: slice it into rectangles, find each area with width × height, and add. Perimeter is a different animal - it is the distance an ant walks all the way round the outside, so the cut you drew does not count. That is why area and perimeter almost never match.
Helping a child through Area Unfolder
It runs in 2 steps
- 1. Slice it. Cut the shape into two rectangles, then add their areas.
- 2. The ant walk. Walk the ant right round the edge. How far did it travel?
Hints, least revealing first
- Drag along one of the faint grid lines inside the shape to make your cut.
- A good cut leaves two neat rectangles - no L-shaped leftovers.
- Area adds up when you cut. Perimeter does not: cutting makes new edges that were never on the outside.
When they finish it: “Nice work!”
2 11+ skills this exercise practises
Each of these has its own page, with a worked example on it. 1 of the 2 names the mistake that skill attracts.
- Calculate areaCalculate the area of a rectangle or decomposable rectilinear shape.
- Calculate perimeterCalculate the boundary length of a labelled rectilinear or polygonal shape.
You can reuse this. Here is exactly how far that goes
Tutors, teachers and editors keep asking, so this is the answer in writing rather than by email. You do not need to ask permission, and you do not need to tell us.
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Embed this exercise
Paste this into your own page and the exercise runs there, playable, for your readers or your students. It is 900 pixels tall by default and as wide as the column you put it in; change the height if your layout wants a different one.
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One exercise is a start, not a plan
A free diagnostic across all four subjects shows which maths skills to practise next, and in what order.