How to Calculate the Diameter of a Bike Seat Post

• Step # 1 – Cut out a small strip of paper, say 1″ wide by 12″ long



• Step # 2 – Wrap this paper strip around the seat post;



• Step # 3 – Mark the both sides of the paper strip with a pencil;



• Step # 4 – Unfurl the strip and measure the distance between 2 marks;



• Step # 5 – Use this equation:
• Diameter (D) = Circumference (C) / Pi

For example, our circumference measured 3.4 inches, we would calculate the diameter this way:

D = 3.4″ / Pi
= 3.4″ / 3.14
= ~1″

So our diameter would round up to 1″.