How to Measure Hub PCD (Pitch Circle Diameter) Correctly

Measuring the Pitch Circle Diameter (PCD) is one of the most important steps when calculating spoke length and building a wheel. PCD refers to the diameter of the imaginary circle that passes through the center of all spoke holes on a hub flange. Accurate measurement ensures correct spoke length, proper tension balance, and a structurally strong wheel.

What You Need

Digital calipers

A ruler (optional)

Clean hub flanges for accurate contact points

What PCD Means

PCD (Pitch Circle Diameter) represents the distance across the circle formed by the spoke holes. Each hub usually has two PCD values — one for the left flange and one for the right flange. These values are essential inputs for any spoke-length calculator.

How to Measure Hub PCD

Method 1: Direct Opposite-Hole Measurement (Most Accurate)

Identify two spoke holes directly opposite each other on the flange.

Place the calipers inside the centers of both holes.

Measure the center-to-center distance.

The result is the flange’s PCD.

This method is the simplest and delivers the best accuracy.

Method 2: Adjacent Hole Measurement (When Opposite Holes Are Hard to Reach)

Measure the distance from the center of one spoke hole to the center of the next.

Count the number of holes on the flange.

Use the formula:
PCD = (Distance between adjacent holes) ÷ sin(180° ÷ Number of holes)

This method is useful when hub geometry prevents direct opposite-hole measurement.

Method 3: Outside-to-Outside Measurement

Measure the outside edge of one hole to the outside edge of the opposite hole.

Measure the diameter of a single spoke hole.

Subtract the hole diameter from the first measurement.

The remainder is the PCD.

This method works best when the spoke holes have clean, uniform edges.

Tips for Accurate Measurement

Take multiple measurements and use the average.

Avoid measuring chamfered or angled edges.

Make sure the hub is clean so the calipers can rest accurately.

Measure both flanges — the left and right PCD values are often different.

Typical PCD Ranges for Reference

You can copy this table directly into Word:

Hub Type	Left PCD (mm)	Right PCD (mm)
Road Front Hub	30–40	30–40
Road Rear Hub	38–45	45–55
Gravel Rear Hub	38–45	50–60
MTB Rear Hub	40–55	55–65

Why PCD Accuracy Matters

Ensures correct spoke length

Helps maintain even spoke tension

Prevents spoke stress, cracking, or premature failure

Ensures compatibility with different lacing patterns

Results in a more reliable and durable wheel build