Getting the hardness of your rubber components exactly right is a fundamental part of a successful product.
In a manufacturing setting, the performance of a final assembly often hinges on the physical properties of its smallest parts. From our position in the industry, we know that a seemingly minor deviation can lead to significant problems. That's why it is so important to have a clear picture of the two primary methods for measuring material firmness, a topic often simplified to IRHD vs Shore.
These two approaches are the established ways to get a value for hardness, and they are both vital in modern quality control. However, they are not interchangeable. Knowing how and when to use each is a key piece of knowledge that separates a good quality process from a great one.
IRHD vs Shore: How These Two Measurement Methods Function
These two ways of checking hardness both produce a number, but they arrive at that result through different mechanical processes.
The mechanical difference is the key to the entire IRHD vs Shore discussion. This is a critical point of friction for teams who might assume the values can be swapped one-for-one without consequence.
Shore Durometers
This method uses a spring-loaded indenter that is pushed into the rubber. How deep that tip penetrates the surface gives you the hardness value.
The most common scales are Shore A, for softer materials, and Shore D, for harder materials. The portability and speed of our Qualitest Shore Durometers make them the proper tool for immediate checks right on the production floor, offering instant feedback without creating a bottleneck.
IRHD Testers
This is a more controlled, precise instrument typically used in a lab setting. It uses a spherical tip that is first applied with a light "minor" load to establish a zero-point, then a heavier "major" load is applied. The difference in indentation depth is what determines the hardness. This two-stage process removes surface irregularities from the equation. For laboratory work that requires data you can depend on, we believe the results from our IRHD Hardness Tester lineup are more consistent.
The physical difference in the instrument tips—the Shore's pointed cone versus the IRHD's rounded ball—is a useful way to remember their primary roles in the IRHD vs Shore debate. One is for direct, rapid assessment; the other is for controlled, analytical measurement.
Related article: Durometer: Accurate Hardness Testing for Rubber and Plastic
How to Select the Right Instrument for Your Application?
Selecting the correct method in the IRHD vs Shore debate is a function of your specific application, the material's form, and the standards you are required to meet. Based on our experience, here is our guidance with some clear examples:
- For O-rings, seals, or other non-flat components: The IRHD method is, in our opinion, the superior choice. Think of the critical hydraulic seals in aerospace landing gear or the tiny, precise O-rings used in a medical device. On a curved surface, a Shore durometer can give a misleading reading, but the IRHD’s spherical tip is made for that exact job.
- For flat, thick rubber sheets and general production-line checks: We consistently recommend a Shore durometer. Consider the thick rubber on a conveyor belt or an anti-vibration pad for industrial machinery. For these applications, you need a fast, reliable reading to confirm a batch is within spec, and a Shore instrument provides that immediate feedback.
For compliance with specific standards (ISO, ASTM): The standard dictates the method. For instance, the widely-used automotive standard ASTM D2240 explicitly calls out the procedure for Shore testing. If your client requires adherence to that document, the choice is already made for you. We build our equipment to be fully compliant with these governing standards.
Related article: Elevating The Quality of Rubber Samples: Qualitest's Solution for Sika's Testing Needs
A Word of Caution on Conversion Charts like an IRHD to Shore A Conversion Table
While you will find tables online that offer conversions, they should not be treated as a substitute for direct testing. We have seen quality issues arise from teams relying on these approximations for final validation. This is why any irhd to shore a conversion table or irhd to shore d conversion table must be used with caution.
The reason is simple: the pointy Shore indenter and the rounded IRHD ball stress the material in different ways. Two materials could have the same Shore A value but show different IRHD readings due to their unique chemical composition. For any application where the result truly matters, using the correct instrument is the only way to be certain.
Below is a standard irhd to shore a conversion table for general reference.
| IRHD | Approximate Shore A |
|---|
| 40 | 39 |
| 50 | 49 |
| 60 | 62 |
| 70 | 68 |
| 80 | 80 |
| 90 | 90 |
Disclaimer: This table is for estimation purposes only.
Similarly, this irhd to shore d conversion table provides approximations for harder materials.
| IRHD | Approximate Shore D |
|---|
| 85 | 33 |
| 90 | 39 |
| 95 | 46 |
| 100 | 58 |
Disclaimer: This is an approximation. Use a dedicated Shore D instrument for accurate measurements.
Solve IRHD vs Shore with Qualitest
Ultimately, we provide more than just equipment; we provide confidence in your results. We know that selecting the right material is just the first step—verifying its properties with the right instrument is how you protect your quality standard. Our full range of durometers and hardness testers is built to meet the real-world needs of our clients.
Don't let inconsistent hardness data or confusion over IRHD vs Shore put your product's performance at risk. Investing in the correct testing procedure is far more cost-effective than dealing with a single product recall. Contact us to discuss the specific challenges you face. Our team of experts will help you find the perfect, cost-effective solution to solidify your quality control process.