This bolt tightening torque calculator helps you estimate the required torque when manufacturer specifications are unavailable. It uses the standard bolt torque equation T = K × D × F to compute an approximate torque for screws, bolts, and nuts.
1) Pick a system (metric or inch), then the bolt or screw diameter.
2) Strength class: choose the closest matching grade/material. Higher yield strength generally means higher allowable preload and torque. Our bolt strength calculator supports ISO, SAE, ASTM, and stainless steel grades.
3) Friction factor K: this is the biggest real-world uncertainty in bolt tightening torque calculation. Lubrication, coatings, thread condition, and washers can change K significantly.
4) % of yield load: for non-critical bolts, conservative values (for example 60-70%) are often safer than pushing to the limit. This affects the bolt stress and resulting preload.
5) Thread type: affects the stress area (As) used in the estimate. Fine threads have slightly larger stress areas than coarse threads.
Practical notes:
- For critical joints (brakes, steering, suspension, engine internals, safety-related fasteners), use manufacturer procedures and applicable standards.
- Torque is not the same as preload; torque is just a proxy and depends heavily on the friction factor K.
- This fastener torque calculator works for both bolt heads and nuts—use the same diameter and grade for accurate nut torque calculations.
- When unsure, use a lower percentage and verify by inspection and re-torque checks if appropriate.
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