Bolt Torque & Tension Calculator
Estimate metric bolt tensile stress area, target preload and installation torque using a user-selected nut factor.
“The fitters are installing M24 bolts. What torque should I place on the drawing?”
Bolt torque and preload reference
A_s = (π/4)(d − 0.9382 p)²F = A_s × σ_proof × preload%T = K F dK is a torque coefficient influenced by friction, lubrication, coatings and the bearing surface.
Preloaded bolt
Choose the bolt
Common metric coarse-thread sizes fill diameter and pitch automatically.
Choose the bolt strength and target preload
Property-class values are editable starting points. Verify the actual fastener specification and certificate.
Choose the friction condition — this sets K
K is a torque coefficient. It is not the bolt grade and it is not a safety factor.
Use “I do not know” when the actual bolt, nut, washer, coating and lubricant combination has not been verified. Read the torque band, not only the centre value.
Use a preset only for preliminary screening. For a critical joint, use supplier data, an approved tightening procedure, or test the actual installation combination.
Torque-tension estimate
Same target preload across the entered low/high K values.
Shows why friction assumptions matter.
The same calculated target preload gives a wide torque range because friction condition has not been established.
Torque control is highly sensitive to friction and installation condition. For critical joints, establish the torque-preload relationship for the actual bolt, nut, washer, coating and lubricant combination.
Approximate metric tensile stress area followed by target preload from the entered proof stress, then T = KFd. This calculator does not check joint separation, bolt fatigue, thread stripping, slip, prying or combined loading.
Save the calculation, not just the number.
Copy a permalink that reloads these inputs, or download a PDF record with inputs, visible results, assumptions, a sensitivity note, date and disclaimer.
A calculator can show the arithmetic. It cannot establish every requirement that applies.
Confirm the actual equipment, loading, materials, condition, jurisdiction, contractual requirements, standard edition and current project documentation before using the result for design, repair, testing or lifting decisions.
Ask an engineer about this calculation →