Bolt Torque Calculator
Find the recommended tightening torque for a bolt by size and grade.
Recommended torque
50.45 N·m
37.21 ft-lb
Tensile stress area: 57.99 mm²
Clamp load (preload): 25.23 kN
Usage examples
Checking bolt torque during equipment assembly
Before using a torque wrench, check the appropriate torque for a bolt's size and grade ahead of time.
Comparing torque between dry and lubricated conditions
See how much the required torque for the same bolt changes between a dry and a lubricated or plated condition.
Working on a job site with mixed metric and imperial bolts
Quickly look up torque values in both systems when a project mixes metric and UNC imperial bolts.
Frequently asked questions
Is this torque value exactly right for every situation?
No. The result is an estimate based on common engineering guidelines (75% of proof load, a standard nut factor). Actual required torque varies with fastening conditions, surface finish, and washer use — for critical joints, defer to the manufacturer's torque spec or an engineering review.
Why does lubrication change the torque needed?
Lubrication or plating reduces friction at the threads and bearing surface, so less torque is needed to reach the same clamp load. This calculator assumes a nut factor (K) of 0.20 dry and 0.16 lubricated/plated.
What do bolt grades like 8.8 or 10.9 mean?
They're ISO 898-1 proof stress classes. A higher number means a stronger material that can tolerate a greater clamp load (and therefore torque).
Why does the result differ slightly from other online torque charts?
That's normal — different sources assume slightly different nut factors or target preload percentages. Cross-check multiple sources and stay within a safe margin.