How is the strength (force) of a clarinet reed determined? 

Clarinet reeds are offered in different strengths. The most common are numerals in half steps/half degrees. For the selection of the reeds, the force required to make the reed vibrate is measured. 

This force is measured by means of a bending beam force sensor. The clarinet reed is pressed onto a force sensor and the spring force/elasticity of the reed is measured. Depending on the hardness of the cane, different forces act on the sensor. After the measurement, the reeds are assigned to the pre-defined strengths. 

The selection of clarinet reeds in strengths always leads to a fundamental misunderstanding, since strength is often associated with the thickness of the vamp or cut of the reed. However, it is only the hardness of each naturally grown piece of cane that determines the elasticity of a reed. Within the same model, the thickness of the vamp or cut of the reed is absolutely identical for all strengths!