Circumference of a Circle Worksheets
Free printable circumference of a circle worksheets: find the distance around a circle from its radius or diameter, using 3.14 for pi. With an answer key.
Each problem draws a circle with one line through it, labelled in centimetres, and asks for the circumference: the distance around the circle. The line is a radius, from the centre dot to the edge, on about half the circles, and a diameter, all the way across, on the rest, so the student has to notice which one they were given. Every question says to use 3.14 for pi.
The circumference is pi times the diameter, C = 3.14 × d. A circle with a radius of 5 cm has a diameter of 10 cm, so its circumference is 3.14 × 10 = 31.4 cm. The slip these sheets are built to catch is multiplying a radius by 3.14 and stopping, which gives half the answer.
The radius is a whole number from 1 to 10 by default, so a diameter on the page is always even and every answer has at most two decimal places. The settings can move the largest radius to 5 or 20. Every circle is drawn the same size, so the label gives the length, never the picture.
What this worksheet covers
- Find the circumference of a circle from its radius
- Find the circumference of a circle from its diameter
- Use 3.14 for pi and give the answer in centimetres
Common Core standards
- 7.G.B.4 Know the formulas for the area and circumference of a circle and use them to solve problems.
Frequently asked questions
What is the circumference of a circle?
The distance around it, the way perimeter is the distance around a polygon. It is always a little more than three times the diameter, and that ratio, which never ends, is pi.
What is the formula for circumference?
C = pi × d, or the same thing written with the radius, C = 2 × pi × r. Using 3.14 for pi, a circle 10 cm across has a circumference of 3.14 × 10 = 31.4 cm.
What if the problem gives the radius?
Double it to get the diameter first. A radius of 7 cm means a diameter of 14 cm, and the circumference is 3.14 × 14 = 43.96 cm.
Why does the sheet say to use 3.14 for pi?
Pi has no last digit, so an answer depends on how many digits are used. Telling every student to use 3.14 gives each circle one answer, with no more than two decimal places. A calculator's pi button gives a slightly different number: for a circle 10 cm across it shows 31.42 where the key says 31.4, so an answer from one will not match the key exactly.