This key facts covers Key Facts within Perimeter for GCSE Mathematics. Revise Perimeter in Geometry & Measures for GCSE Mathematics with 10 exam-style questions and 2 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 2 of 5 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Key Facts
| Perimeter | Total distance around the outside of a shape |
| Rectangle | P = 2(l + w) or 2l + 2w |
| Square | P = 4s (4 × side) |
| Triangle | P = a + b + c (add all 3 sides) |
| Circle | Circumference = πd = 2πr |
| Units | Linear units (cm, m, km) - NOT squared! |
Practice questions for Perimeter
What is the perimeter of a shape?
Two similar rectangles have lengths in the ratio 3:5. The perimeter of the smaller rectangle is 24 cm. Explain how to find the perimeter of the larger rectangle without knowing its individual dimensions.
Quick recall flashcards
Perimeter vs Area
Perimeter = distance AROUND (1D - cm, m). Area = space INSIDE (2D - cm², m²).
Perimeter
Total distance around a shape, add all sides