How do I measure the size of a bike frame?
Bike frames are measured from the centre of the crank to the top of the seat post tube.
Place the end of a tape measure at the exact centre point of the crank bolt, then run the tape measure to the top of the seat post tube.
This will give you the length of the seat tube which indicates the size of the frame. In most cases frame sizes are measured in inches such as 16", 18", 20" and so on.