How to calculate tightening torque
The fetched OmniCalculator bolt torque page relates torque, bolt diameter, clamping force, and lubrication with this approximation:
T = K x F x d x (1 - l / 100)
Here, T is tightening torque, K is a bolt constant, F is the clamping force, d is bolt diameter, and l is the lubrication factor in percent.
Using the calculator both ways
Omni explicitly notes that the same tool can work in reverse. If you know the clamping force requirement, you can solve for torque. If you already know the torque setting, you can back-calculate the implied clamping force.
Source-backed example
The fetched example uses a zinc-plated mild-steel bolt, 3/4-inch diameter, SAE 30 oil, 40% lubrication factor, 25,000 lb of clamping force, and arrives at approximately 187.5 lbf-ft of torque. That example is preloaded in this rebuild.