Bolt Torque Calculator

Your details

Switches diameter, force, and torque units throughout.
Normal mode: enter a target clamping force and get the required torque. Reverse mode: enter a known torque and get the resulting clamping force.
ISO metric bolt size. Selecting a size sets the nominal diameter and tensile stress area used for preload calculation.
ISO 898-1 property class. Used to calculate the proof-load-based preload when the preset clamping force option is selected.
Override the diameter from the size preset with a custom value.
Nominal bolt diameter used in the torque formula.
mm
Sets the nut factor K that captures thread and bearing friction. A lower K means less torque is lost to friction, so the same torque produces more clamping force.
Fraction of the bolt proof load used as the target clamping force. 75% is the standard recommendation for most structural joints. Increase to 85-90% for torque-to-yield (TTY) applications.
Override the proof-load-based preload with a specific clamping force.
Target axial clamping force (preload) in newtons.
N
Tightening torqueGood preload range
52.2

Required tightening torque for the target clamping force

Torque unitN·m
Clamping force (preload)26,096
Force unitN
K-factor used0.2
Diameter used10
Diameter unitmm
Bolt tensile stress450
Stress unitMPa
Proof load utilization75%
75% % of proof
Under-loaded<50%Good preload50%-85%High preload85%-95%Exceeds proof95%+

Required torque: 52.2 N-m

  • The required tightening torque is 52.2 N-m, producing a clamping force of 26,096 N.
  • Bolt tensile stress is 450.0 MPa, which is 75% of the proof load.
  • With K = 0.20 (dry steel), consider that friction can vary up to 25% in practice. A torque audit on a sample joint is recommended for critical applications.
  • Never use these values for safety-critical joints (engine heads, structural steel connections, pressure flanges) without consulting a qualified engineer and the OEM specification.

Next stepSet your torque wrench to 52.2 N-m and tighten in a cross-pattern using 3 passes: 50%, 80%, then 100% of the target torque.

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