How to Know the BCD (Bolt Circle Diameter) of Your Chainrings?

The BCD (Bolt Circle Diameter) is the diameterof a circle passing through the center of all chain rings bolts holes.
It's one of the most important information to know if a chain rings fit on a crank set or not.
5 Arms Chainrings
On a 5 arms chain rings, you have to measure the distance between two neighbor bolt holes from center to center.
Use the measurement to find your BCD on the table below:

34.1 mm | ![]() | 58 mm |
43.5 mm | ![]() | 74 mm |
50.6 mm | ![]() | 86 mm |
55.3 mm | ![]() | 94 mm |
64.7 mm | ![]() | 110 mm |
71.7 mm | ![]() | 122 mm |
76.5 mm | ![]() | 130 mm |
79.4 mm | ![]() | 135 mm |
84.7 mm | ![]() | 144 mm |
4 Arms Chainrings
On a 4 arms chain rings, you have to measure the distance between twoopposite bolt holes from center to center.

64 mm | ![]() | 64 mm |
76 mm | ![]() | 76 mm |
80 mm | ![]() | 80 mm |
94 mm | ![]() | 94 mm |
102 mm | ![]() | 102 mm |
104 mm | ![]() | 104 mm |
120 mm | ![]() | 120 mm |
146 mm | ![]() | 146 mm |
Please note: Shimano Dura-ace FC-9000 / Ultegra FC-6800 / 105 FC-5800 & SRAM XX1 cannot be measured like this because of the asymmetrical placement of bolt holes.