Enter the material constant, the nominal bolt diameter (ft), lubrication factor, and the axial bolt force (lbf) into the calculator to determine the Screw Torque. 

Screw Torque Formula

The following formula is used to calculate the Screw Torque.

Ts = K*F*d * (1-L / 100)

  • Where Ts is the Screw Torque (lb-ft)
  • K is the material constant 
    • .2 for normal steel bolts from .250″ to 1″
  • d is the nominal bolt diameter (ft) 
  • F is the axial bolt force (lbf) 
  • L is the force lost due to lubrication (%)

How to Calculate Screw Torque?

The following example problems outline how to calculate Screw Torque.

Example Problem #1

  1. First, determine the material constant. In this example, the material constant is determined to be .2 .
  2. Next, determine the nominal bolt diameter (ft). For this problem, the nominal bolt diameter (ft) is measured to be .25.
  3. Next, determine the axial bolt force (lbf). In this case, the axial bolt force (lbf) is found to be 1000.
  4. Next, determine the loss due to lubrication. In this example, this is 50%.
  5. Finally, calculate the Screw Torque using the formula above: 

Inserting the values from above and solving yields: 

Ts = K*F*d * (1-L / 100) = (lb-ft)

Ts = .2*1000*.25 * (1-50 / 100) = 25 lb-ft

Example Problem #2

Using the same method as above, determine the variables required by the formula. For this example problem, these are:

material constant = .2

nominal bolt diameter (ft) = .3

axial bolt force (lbf) = 5000

lubrication loss (%) = 35

Enter these given values into the calculator or above yields: 

Ts = .2*5000*.3 * (1-35 / 100) = 195 (lb-ft)