Geometry
Mixing Up Perimeter and Circumference Formulas
Students use a polygon perimeter formula when the shape is a circle, or they use when the shape is not a circle.
Quick check
Why students make it
The words perimeter and circumference both mean distance around a shape, so students treat the formulas as interchangeable. They may also grab a familiar formula before checking whether the shape is a polygon or a circle.
The rule done right
Use perimeter for polygons by adding all side lengths. Use circumference for circles, or , where .
Related resources
-
Geometry, Circumference of a Circle Infographic -
Geometry, Perimeter and Circumference Review Infographic -
Geometry, Perimeter of Polygons Infographic -
Area & Perimeter Infographic -
Geometry, Area of a Circle Infographic - Circles Cheat Sheet
- Circle circumference and area formulas Memory Aid Cheat Sheet
- Perimeter is the distance around the edge Memory Aid Cheat Sheet
- Area & Perimeter Reference Cheat Sheet
- Polygons & Quadrilaterals Cheat Sheet
- Geometry, Circles (Middle School) Worksheet
- Circle Circumference and Area Formulas Practice Worksheet
- Math, Circles, Radius, Diameter, Circumference Worksheet
- Geometry, Perimeter is the Distance Around the Edge Practice Worksheet
- Measuring Perimeter with a Ruler Worksheet
- Area & Perimeter Explorer Tool
- Polygon Properties Calculator Tool
- Circle Theorems Explorer Tool
- Shape Classifier Lab Lab
- Polygon Explorer Lab Lab
- Area & Perimeter Design Challenge Lab
- Circle Theorems & Tangency Lab Lab