Enter the torque applied to the bolt, the diameter of the bolt, and the coefficient of friction for the bolt contact to determine the clamping force.

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## Clamping Force Formula

The following formula is used to calculate the axial clamping force of a bolt.

F = T / K * D

- Where F is the clamping force (N, lbs)
- T is the torque applied to the bolt (N-mm, in-lb)
- K is the friction of the bolt contact
- Steel = .2
- Cadmium = .161
- Lubricated = .17

- D is the diameter of the bolt ( mm, in )

To calculate clamping force, divide the bolt torque by the bolt friction constant, then multiply by the diameter of the bolt.

## Clamping Force Definition

**What is a clamping force? **A clamping force is a measure of the force applied to an object that is used to oppose separating forces that are trying to move that object from its current location.

## Example Problem

How to calculate clamping force?

**First, determine the torque applied to the bolt.**Using a torque wrench, the torque being applied to the bolt in this example is found to be 300 in-lbs.

**Next, determine the diameter of the bolt.**The bolt being used in this application is a measure to be 2 inches.

**Next, determine the friction of the bolt.**In this example, the bolt is a standard steel bolt. The friction is assumed to be .2. In reality, this could vary slightly depending on several factors, but .2 is a good estimate.

**Finally, calculate the clamping force.**Using the formula, the clamping force is found to be 300/(2*.2) = 750 lbs of force.

## About Clamping Force

**What is clamping force measure in? **A clamping force is typically measured using units of lbs or newtons. Clamping forces use the same units as any other force metric.

**Does clamping force increase with the number of bolts? **Increase the number of bolts on a fixture will increase the clamping force. Typically the total clamping force would be approximately the sum of each of the clamping forces provided by the individual bolts.

**How much clamping force do I** need? One way to determine how much clamping force you need is to first determine a factor of safety. That is how much more than the exact required amount you want to design for. In general, a factor of safety of 2 or more is recommended. Next, determine the exact force that the object may see during operation and then multiply by the factor of safety.