Bolt Torque Calculator

About the Bolt Torque Calculator

Calculates the tightening torque needed to achieve a target bolt preload (clamp force), using the nut factor K and bolt diameter.

How to use this calculator

1. Enter the target preload force in \(\text{N}\) or the unit used by your calculator.
2. Choose the torque coefficient \(K\), which represents friction in the threads and under the head.
3. Enter the bolt diameter \(d\). Make sure the units match the force units so the torque comes out correctly.
4. Read the calculated torque \(T\), then apply it with a torque wrench and check the joint specification.

The formula explained

The formula \(T = K \cdot F \cdot d\) estimates the tightening torque needed to create a target preload. It combines the preload force \(F\), the bolt diameter \(d\), and the torque coefficient \(K\), which accounts for friction.

• T = tightening torque
• K = torque coefficient, a friction factor
• F = target bolt preload force
• d = bolt diameter

Step by step method

1. Identify the target preload force \(F\), the bolt diameter \(d\), and the torque coefficient \(K\).
2. Substitute the values into \(T = K \cdot F \cdot d\).
3. Multiply \(K\), \(F\), and \(d\) to find the torque.

Worked example

Problem. Find the tightening torque for a bolt with preload \(F = 12{,}000\) \(\text{N}\), torque coefficient \(K = 0.20\), and diameter \(d = 0.010\) \(\text{m}\).

1. Start with \(T = K \cdot F \cdot d\).
2. Substitute the values, \(T = 0.20 \cdot 12{,}000 \cdot 0.010\).
3. Compute the result, \(T = 24\) \(\text{N}\cdot\text{m}\).

Tips and common mistakes

• The coefficient \(K\) can change a lot with lubrication, coating, and surface condition, so use the value from your engineering data when possible.
• Torque is only an estimate of preload, because friction can vary from bolt to bolt.

Frequently asked questions