Geometry guide
Area or perimeter: how to tell which one you need
Area measures the surface inside a shape. Perimeter measures the distance around its boundary. Before calculating, underline what the question asks you to cover, fill, fence, frame, or walk around.
Grades 3–5 · worked example · 3 practice checks
01
Recognize the problem first
- Covering, tiling, painting, or filling a surface usually asks for area.
- Fencing, edging, framing, or travelling around a shape usually asks for perimeter.
- Area uses square units such as cm²; perimeter uses length units such as cm.
02
Work through one complete example
Question
A rectangular garden is 8 m long and 5 m wide. Find both its planting area and the length of fence around it.
- For the planted surface, multiply length by width: 8 × 5 = 40.
- For the boundary, add all four sides: 8 + 5 + 8 + 5 = 26.
- Attach the correct units: square metres for area and metres for perimeter.
AnswerArea = 40 m²; perimeter = 26 m.
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03
Common mistakes to catch
- Adding 8 + 5 and calling 13 the perimeter; that counts only two sides.
- Writing m instead of m² for area.
- Using a formula before deciding whether the question concerns the inside or the boundary.
0401 02 03
Try three quick checks
A 7 cm by 4 cm card is covered with paper. How much paper is needed?
Show answer
28 cm²A 9 m by 3 m pen needs fencing. How much fence is needed?
Show answer
24 mA square has side length 6 cm. Find its area and perimeter.