Enter the torque, bolt diameter, and nut factor into the calculator to determine the clamp load. This calculator helps in understanding the force exerted by a fastener when tightened.

Clamp Load Calculator

Enter any 3 values to calculate the missing variable

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Clamp Load Formula

The following formula is used to calculate the clamp load (using consistent SI units).

CL = T / (K * D)

Variables:

  • CL is the clamp load (N)
  • T is the torque applied to the fastener (N·m)
  • D is the nominal diameter of the fastener (m)
  • K is the nut factor (dimensionless). A common assumption is K ≈ 0.20, but it varies significantly with lubrication and surface condition (often roughly 0.15–0.25).

To calculate the clamp load, divide the torque applied to the fastener by the product of the nut factor (K) and the nominal diameter of the fastener (D). If you use D in millimeters, then CL(N) = (1000 × T) / (K × D(mm)) (equivalently, CL(kN) = T / (K × D(mm))).

What is Clamp Load?

Clamp load, also known as preload, is the tension generated in a fastener when it is tightened. This load is critical in ensuring that the fastener does not loosen under operational conditions. It is the force that holds together the components being fastened, preventing separation or sliding. The clamp load must be properly calculated to ensure joint integrity without over-tightening, which can lead to fastener or material failure.

How to Calculate Clamp Load?

The following steps outline how to calculate the Clamp Load.

  1. First, determine the torque applied to the fastener (T) in Newton-meters (N·m).
  2. Next, determine the nominal diameter of the fastener (D) in meters (m) (or convert from mm to m by dividing by 1000).
  3. Next, determine the nut factor (K) for the joint/fastener condition (a common assumption is 0.20, but it depends on friction and lubrication).
  4. Finally, calculate the Clamp Load (CL) in newtons (N) using the formula CL = T / (K * D).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

torque applied to the fastener (T) = 50 N·m

nominal diameter of the fastener (D) = 10 mm (0.010 m)

nut factor (K) = 0.20

Clamp Load (CL) = 50 / (0.20 × 0.010) = 25,000 N = 25 kN