Enter the nominal diameter (in), the desired clamp load (lbf), and the coefficient of friction into the calculator to determine the Fastener Torque. 

Fastener Torque Formula

The following formula is used to calculate the Fastener Torque.

Tf = (D*P*K) / 12
  • Where Tf is the Fastener Torque (lbf-ft)
  • D is the nominal diameter (in) 
  • P is the desired clamp load (lbf) 
  • K is the coefficient of friction 

To calculate a fastener torque, multiply the nominal diameter, desired clamp load, and coefficient of friction, then divide by 12.

How to Calculate Fastener Torque?

The following example problems outline how to calculate Fastener Torque.

Example Problem #1

  1. First, determine the nominal diameter (in). In this example, the nominal diameter (in) is determined to be .25 .
  2. Next, determine the desired clamp load (lbf). For this problem, the desired clamp load (lbf) is measured to be 500 .
  3. Next, determine the coefficient of friction. In this case, the coefficient of friction is found to be .85.
  4. Finally, calculate the Fastener Torque using the formula above: 

Tf = (D*P*K) / 12

Inserting the values from above and solving yields: 

Tf = (.25*500*.85) / 12 = 8.85 (lbf-ft)


What factors can affect the coefficient of friction in fastener torque calculations?

The coefficient of friction can be affected by several factors including the material of the fasteners and mating surfaces, the presence of lubrication, surface finish, and even the temperature at which the fastening occurs. Different materials and surface conditions can significantly alter the coefficient of friction, thus impacting the torque required.

How does the nominal diameter of a fastener influence its torque requirements?

The nominal diameter of a fastener directly influences the torque requirements because it determines the amount of surface area in contact between the fastener and the material it is securing. A larger diameter means a larger contact area, which can distribute the clamp load more effectively. This, in turn, can affect the amount of torque needed to achieve the desired clamp load without causing damage to the fastener or the material.

Why is it important to accurately calculate fastener torque?

Accurately calculating fastener torque is crucial for several reasons. First, it ensures that the fastener is tightened sufficiently to prevent loosening under operational conditions, which can lead to failure of the assembly. Second, it helps avoid over-tightening, which can cause damage to the fastener or the materials being clamped, potentially leading to failure under stress. Proper torque calculation ensures the reliability and longevity of the assembly while maintaining safety standards.