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 … [Read more...] about How to Calculate the Diameter of a Bike Seat Post