How to Measure Bottom Bracket of Your Bike

Want to learn how to measure the bottom bracket? Then read on! The bottom bracket of your bike is located in the part that connects the seat with the frame’s down tubes.

It’s characterized by a duo of bearings that are positioned in a manner that enables the free rotation of chainrings and pedals.

Due to their function, bottom brackets are typically constructed from the best and most durable materials so that they can withstand the elements. That’s why you must be careful when learning how to determine bottom bracket size.

With that said, they’re also available in different types of designs in order to cater to different bike models and manufacturers.

Read on as we show you what measuring the bottom bracket takes and what you need.

How to Determine Bottom Bracket Size

The key is to ensure that you use the proper tools for the job like would you do when you mount your bicycle on a bike rack for carbon bike. This will make it possible to ensure accurate bottom bracket measurements.

Here are the main tools you’ll need when you learn how to measure bottom bracket size:

  • Calipers or metric rulers
  • A spindle

1. Check Everything

First things first, it’s important to note that the part of the bottom bracket where the spindle is requires regular changing.

This means that you’re going to have to measure the components each and every time you do this.

Note also that bottom bracket measures are usually expressed in mm which is why it’s recommended to use calipers or a metric ruler to get an accurate measurement.

2. Measure the Shell

The second step is to take your bike and flip it upside down so that you can start measuring it by placing the ruler or calipers against the casing of the bike.

The point here is to get a measurement of the shell’s length from end to end excluding the internal part of the spindle.

Most bottom bracket shells have measurements of either 68, 70, or 73 mm.

3. Measure the Spindle

Another key to learning how to measure bottom bracket spindle length is to remove the crank arms so that you can ensure that you get an accurate measurement.

That’s because removing the crank arms allows you to get an end-to-end measurement of the spindle’s length, again in millimeters.

Be sure to exclude the parts of the spindle that are attached with bolts in your measurement if you want a truly precise measurement.


Those are the basics of how to measure the bottom brackets of your bike, using very simple and accessible tools that you probably have in your garage or shed.

This won’t take longer than several minutes at most. Once you have that measurement, you’ll be able to then use it to replace the parts that you need and actually get the right components for your bicycle, which will, in turn, allow for optimal performance!

Have fun out there!

Shailen Vandeyar

A proud Indian origin Kiwi who loves to plant trees and play with my pet bunny when not out cycling through the best routes, reviewing the latest gear, and sharing tips on everything biking.

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