AutoEngCalc - Engineering Calculators

Bolt Torque Calculator

Calculate required tightening torque for bolts to achieve target preload. Includes K-factor, friction, thread/head contribution and safety check.

Required Torque
352 Nm
M16 Grade 12.9, 75% preload, K=0.18

Bolt Torque & Preload

Featured: K-Factor Method, Thread/Head Friction, Proof Load

Torque vs Preload % for Different K-Factors

Shows how lubrication reduces required torque dramatically

Industry standard empirical method (fast & reliable).

T = K × P × d
P = Preload Force (N)

Enter parameters and click Calculate

Bolt Torque Guidelines

Typical K-Factors

  • Dry steel: 0.20–0.30
  • Light oil: 0.15–0.18
  • MoS₂ paste: 0.10–0.13
  • Zinc plated: 0.18–0.22

Safe Preload Levels

  • Reusable joints: 70–80%
  • Structural bolts: 85–90%
  • High-strength: 90–95%
  • Never exceed 100%
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