Occasionally we get asked about how to calculate tension based on the Sonic Tension Meter frequency measurement. The STM will calculate tension in pounds or Newtons for you with the proper input, but the math behind it is really pretty simple. Here's how to do it by hand:
T = 4 x M x W x S^2 x f^2 x 10^-9
T = Belt span tension
M = Belt mass constant
W = Belt width or number of strands
S = Length of the span to be measured
f = Natural frequency of the belt
Make sure to use proper units!