Use the formula: C = 2πr
Or use the formula: C = πd
Measure the radius if you are using C = 2πr
Measure the diameter if you are using C = πd
Multiply the radius by 2 and then by π
Or multiply the diameter by π
Use π ≈ 3.14 if needed
Keep the units the same throughout
Write the final answer in square units if required by the problem