7.G.1 — Circumference of a circle.
Step 01 of 03
Two equivalent formulas, one using the radius, one the diameter.
The constant is the ratio of every circle's circumference to its diameter.
Step 02 of 03
Radius 5 → .
Diameter 14 → .
Step 03 of 03
Leave answers in terms of for exact values; use only when an approximation is asked.
Key insight
. Same formula written two ways. Diameter is twice the radius — use whichever is given.