Diameter & Tread Width: Ensure the Right Fitment

August 28, 2025

The diameter and tread width of a wheel seem pretty straightforward.... and they are! While we find that many of our customers get the diameter and tread width of their wheels right, there are a few tricks to help confirm your measurements and ensure a proper fit.

This article aims to establish the basics on how to get the right measurements, a few tips to help determine whether your wheel is metric- or standard-sized, and mention some common size practices in the caster industry.

Diameter

A hand measuring the diameter of an orange wheel

To measure wheel diameter, go straight across from one edge of the wheel to the other at its widest point. Keep in mind that worn wheels may be smaller than their original size.

Most caster wheel diameters are in whole numbers, with the exception of 2-1/2 and 3-1/2 inches. Half sizes are rare, and it’s usually safe to round up to the next whole number.

Metric sized caster wheels can be tricky to identify if not labeled. Clues that your caster may be metric include a square top plate, a metric stem, or a metric-sized axle. These often indicate the wheel is metric even if it’s not clearly marked.

Tread Width

A hand measuring the tread wheel of an orange crowned wheel

To measure tread width, measure the width of the part of the wheel that contacts the ground. For rounded and crowned treads, include the full width of the curved surface, even if it doesn't fully touch the ground.

Caster wheel tread widths can be whole numbers, half sizes, and quarter sizes for standard sized wheels. Wheels smaller than 1 inch often use even smaller fractional measurements.

Metric sized tread widths typically differ in 5mm increments: common sizes are 25mm, 30mm, 50mm, and 75mm, and these are used across many applications.

Final Thoughts

Many caster wheels have these key measurements stamped directly on the wheel, making them easy to identify with out the need to measure. However, for wheels that don't their sizes on them, it's better to follow the old carpenter’s saying and "measure twice, cut once". Taking a moment to double-check your measurements can save you time, money and the hassle of returns.

Having trouble measuring your wheels? Have questions or need help choosing the right caster? Contact us at 800-345-0425 (Mon–Fri), 7:00 AM to 4:30 PM CST. We're here to help.

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