How to Measure an O-Ring

Measuring O-Ring Dimensions

Proper measurement ensures you get the right replacement O-ring. Here's how to measure correctly.

Key Measurements

1. Inner Diameter (ID)

The inside opening of the O-ring:

• Use calipers for best accuracy
• Measure at multiple points
• Record the average

2. Cross Section (CS)

The thickness/diameter of the ring material:

• Measure the O-ring "thickness"
• Use a micrometer for accuracy
• Measure at several points around the ring

3. Outer Diameter (OD) - Optional

Calculated as: OD = ID + (2 × CS)

Step-by-Step Guide

1. Place O-ring flat on a clean surface
2. Measure ID with inside calipers or by measuring across the opening
3. Measure CS with outside calipers or micrometer
4. Convert to standard size using AS568 chart

Tips for Accurate Measurement

• Use quality measuring tools (digital calipers preferred)
• Measure at room temperature
• Don't stretch the O-ring during measurement
• Take multiple measurements and average
• Convert to both inch and metric for reference

Common Measurement Mistakes

Mistake	Result	Prevention
Measuring stretched ring	Incorrect ID	Let ring relax
Single measurement	May miss variation	Measure multiple points
Wrong units	Wrong size ordered	Double-check units

Need Help?

If you're unsure about your measurements or can't find a matching standard size:

• Send us photos with measurements
• Describe your application
• We'll help identify the right O-ring

Contact us at support@oxxring.com for technical assistance