How To Measure A BMX Bike Frame

Whether you’re buying a new bike or just looking to replace the frame of an old one, you need to know how to measure a BMX bike frame. The frame should be able to support your weight when you land or do tricks. The right bike frame will be suitable for both your weight and your height. The BMX bike frame's distinctive thick tubing should be measured at four key points to determine if it's the right fit.

To measure the frame, you’ll need:

  • Caliper that measures in inches and millimeters
  • Tape measure
  1. Hold the frame upright to measure the top tube. Find the point where the top tube and seat tube intersect. Find the point where the top tube and the head tube meet. Measure between those two points using the tape measure. For the most accurate measurement, run the tape from the center point of each of  those intersections. Round to the nearest 1/2 inch.
  2. Use the caliper to measure the inside diameter of the head tube. This measurement should be made in inches and will determine the size of the headset. The stem and the fork both go inside the head tube.
  3. Measure inside the bottom bracket shell. Use the caliper to measure, in millimeters, the bottom bracket shell’s inside diameter. The bottom bracket shell is the location of the pedal crank bearings.
  4. Determine the axle size. Measure the open axle slot with the caliper. The axle slot is located in the frame drop out. It is the fork-like area in which the hub axle slides.