Tear strength is the amount of force needed to rip a particular sampling subject and to continue through it in a vertical axis. Typically used for testing of plastic film, plastic sheets and other rubber products, tear strength is calculated by force (in Newtons) divided by thickness (in millimeters, centimeters, inches, etc.): Tear strength = F/t
Most companies that conduct tear strength tests use machines where tears are done at specific levels of force through different sample thicknesses to assure that they are up to the demands placed upon the product.
Determine the amount of force. This should be in the standard measure of Newtons. (Force is calculated by multiplying mass by acceleration, F = ma.)
For example: Force = 28.5 N
Determine thickness of sample used. This can be in millimeters (mm), centimeters (cm), inches (inch), meters (m), etc.
For example: t = 7.2mm
Divide the amount of force by the thickness of the sample. The result will be measured in Newtons per unit of thickness.
For example: 28.5 N/7.2mm = 3.9583 N/mm