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O-Ring Durometer Chart -Hardness

The hardness of rubber o-ring compounds are measured by the Shore A durometer; the higher the durometer, the harder the compound.  70-durometer hardness should be used whenever possible as it offers the best combination of properties for most o-ring applications.

Durometer Shore A scale is a type of measurement for rubber material hardness. The rubber durometer chart below gives you an idea of the rubber hardness that you want for your application. Generally, most rubber materials fall under the rubber durometer scale of Shore A. If you need a rubber or O-ring durometer that feels like a running shoe sole, review our rubber hardness chart below, then pick Shore 70A. A rubber durometer of Shore 70A is the most commonly chosen material hardness for all applications.

  • Duro 20A = Rubber Band
  • Duro 40A = Pencil Eraser
  • Duro 60A = Car Tire Tread
  • Duro 70A* = Running Shoe Sole
  • Duro 80A = Leather Belt
  • Duro 100A = Shopping Cart Wheel

*Most common durometer

Softer compounds stretch easier and seal better on rough surfaces.  Harder compounds offer greater abrasion resistance and resistance to extrusion.  Extrusion must always be considered where high pressure is used.  The proper hardness may be selected from this chart by matching the fluid pressure with the maximum extrusion gap.

  • 60 Shore A is softer than 70.
  • 70 Shore A is the standard.
  • 90 Shore A is very stiff.


O-ring Duro

The hardness of an elastomer is measured based on the depth of indentation by a standard size and shape impacting gauge. The hardness is obtained by comparing the difference between a small initial force and a much larger final force. The International Rubber Hardness Degrees (IRHD) scale has a range of 0 to 100, corresponding to elastic modulus of 0 (0) and infinite (100), respectively. The measurement is made by indenting a rigid ball into the rubber specimen.

The Shore A scale is the most prevalent in the United States. The readings range from 30 to 95 points. Harder elastomers use a pointed conical indentor with the Shore D scale. The results of the Shore A scale and the IRHD scale are approximately equal over the same range of resiliency. In elastomers with unusually high rates of stress relaxation or deformation hysteresis, the difference in dwell time in the two readings may cause different results. Also, the results of any hardness test depend on the elastomer thickness. Specified thickness should be used when conducting these tests.

Due to the mechanical limits of the test instruments, hardness measurements of elastomers are rarely expressed more precisely than 5 points.

The surface indentation or hardness usually does not bear any relation to the ability of an elastomeric part to function properly. Hardness is a measure of an elastomer's response to a small surface stress. Stiffness and compressive modulus measure the response to large stresses of the entire elastomeric part.

Extrusion Gap Pressure Info

Hardness (Shore A) Pressure (PSI)
Below 500 500 - 1000 1000 - 1500 1500 - 2000 2000 - 3000
70 0.016 0.010 0.006 0.004 0.002
90 0.028 0.024 0.020 0.016 0.010


Information within is believed to be accurate and reliable. However, The O-Ring Store, LLC makes no warranty, expressed or implied, that parts supplied in this material will perform satisfactorily in specific applications. It’s the customer’s responsibility to evaluate the material prior to use.