Torque calculators
Six calculators that run on the same data as the torque charts: SAE J429 and ISO 898-1 proof loads, published nut factors and NIST conversion factors. Each one shows its inputs and its formula, so you can check the arithmetic.
Contents4 sections
Key takeaways
- Bolt torque is calculated as T = K × D × F, with F at 75% of proof load, the basis Fastenal uses for its tables 1.
- A torque only means something next to its thread condition: the same bolt needs about 25% less torque oiled (K 0.15) than plain dry (K 0.20) for the same clamp load.
- A torque wrench controls clamp load to about ±25% at best 2. The calculators give a nominal value, not a guarantee.
Which calculator to use
- You know the bolt and want a torque. Use the bolt torque calculator. Pick the size, thread, grade and thread condition.
- You have a dry spec and the threads will be oiled or coated. Use the lubricated torque calculator. It scales by the ratio of nut factors, not by a guessed percentage.
- The number is in the wrong unit. The torque converter handles ft-lb, in-lb, N·m, kgf·m, kgf·cm and ozf·in with the NIST SP 811 factors 3.
- A crowfoot or adapter makes the wrench longer. The extension calculator gives the setting to dial in.
- You know the torque and want the clamp load. The clamp load calculator runs the formula in reverse.
- You don’t know the grade. The grade identifier reads SAE, metric and ASTM head marks.
When a vehicle or equipment maker publishes a torque for the joint, use theirs. The calculators are for fasteners that come without one.
In this section
- Bolt torque calculatorBolt torque calculator for SAE and metric bolts by size, thread, grade and lubrication, using T = K × D × F with the proof loads from SAE J429 and ISO 898-1.
- Lubricated torqueConvert a dry torque spec to oiled, zinc, anti-seize or moly threads by the ratio of nut factors. 100 ft-lb dry becomes 80 ft-lb with copper anti-seize.
- Torque converterConvert torque between ft-lb, in-lb, N·m, kgf·m, kgf·cm and ozf·in. 1 ft-lb = 1.355818 N·m and 1 kgf·m = 9.80665 N·m, from NIST SP 811.
- Bolt grade identificationIdentify a bolt's grade from its head: no marks, 3 or 6 radial lines for SAE Grade 2, 5, 8, stamped numbers for metric 8.8 to 12.9, and A325 or A490 for structural.
- Extension calculatorFind the torque wrench setting with a crowfoot or adapter: T_set = T × L ÷ (L + E). 100 ft-lb through a 2 in adapter on an 18 in wrench means setting 90.
- Clamp load calculatorEstimate bolt clamp load from tightening torque with F = T ÷ (K × D). 75 ft-lb on a 1/2 in bolt with dry threads gives about 9,000 lbf (40 kN), ±25%.
Sources
- 1
- 2
- 3
Spotted a value that doesn’t match its source? Report an error
Related
- MethodologyHow Torque Reference calculates bolt torque from SAE, ISO and RCSC standards and sources vehicle torque from manufacturer documents, with every input listed.
- Dry vs lubricated torqueWhy oiled bolts need less torque than dry ones for the same clamp load, with nut factor K values from Fastenal, NASA and Henkel for oil, zinc, anti-seize and moly.
- Torque vs tensionTorque only estimates bolt tension: about 90% goes into friction, so preload scatters ±25% or more. The figures from NASA-STD-5020B, NASA RP-1228, Fastenal and RCSC.
- Bolt torqueBolt torque for SAE Grade 2, 5, 8 and metric 4.6 to 12.9, 1/4 in to 1 in and M3 to M30, with dry, zinc-plated and lubricated values shown separately.