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Bolt Torque Calculator

Find the right torque for your bolt. Pick a size, grade, and surface condition. This tool gives you torque in ft-lbs and N·m based on 75% proof load.

Calculate Bolt Torque

Pick your bolt size, thread type, grade, and surface condition. Then press Calculate.

Recommended Torque

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ft-lbs
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N·m

Torque Formula

T = K × D × P
  • T = Torque (in-lbs, then converted to ft-lbs)
  • K = Friction factor (nut factor). Dry = 0.20, Oiled = 0.15, Anti-seize = 0.12, Waxed = 0.13
  • D = Nominal bolt diameter (inches)
  • P = Clamp load (lbs) = 75% of proof load. Proof load = proof stress × tensile stress area

Quick Reference Table

Common bolt torque values for dry conditions (K = 0.20) at 75% proof load. Use the calculator above for other conditions.

Showing 50 of 50 rows
Bolt Size ▲ Thread ▲ Grade ▲ Torque (ft-lbs) ▲ Torque (N·m) ▲
1/4"-20UNCGrade 25.57.5
1/4"-20UNCGrade 58.511.5
1/4"-20UNCGrade 81216.3
1/4"-20UNCA2-707.510.2
1/4"-20UNCA4-809.512.9
5/16"-18UNCGrade 21114.9
5/16"-18UNCGrade 51723.1
5/16"-18UNCGrade 82432.5
5/16"-18UNCA2-701520.3
5/16"-18UNCA4-801925.8
3/8"-16UNCGrade 22027.1
3/8"-16UNCGrade 53142.0
3/8"-16UNCGrade 84459.7
3/8"-16UNCA2-702736.6
3/8"-16UNCA4-803547.5
7/16"-14UNCGrade 23243.4
7/16"-14UNCGrade 54966.4
7/16"-14UNCGrade 87094.9
7/16"-14UNCA2-704358.3
7/16"-14UNCA4-805574.6
1/2"-13UNCGrade 24865.1
1/2"-13UNCGrade 575101.7
1/2"-13UNCGrade 8105142.4
1/2"-13UNCA2-706689.5
1/2"-13UNCA4-8083112.5
9/16"-12UNCGrade 26892.2
9/16"-12UNCGrade 5105142.4
9/16"-12UNCGrade 8150203.4
9/16"-12UNCA2-7093126.1
9/16"-12UNCA4-80117158.6
5/8"-11UNCGrade 295128.8
5/8"-11UNCGrade 5150203.4
5/8"-11UNCGrade 8210284.7
5/8"-11UNCA2-70130176.3
5/8"-11UNCA4-80165223.7
3/4"-10UNCGrade 2165223.7
3/4"-10UNCGrade 5260352.5
3/4"-10UNCGrade 8365494.9
3/4"-10UNCA2-70225305.1
3/4"-10UNCA4-80285386.4
7/8"-9UNCGrade 2260352.5
7/8"-9UNCGrade 5400542.4
7/8"-9UNCGrade 8565765.9
7/8"-9UNCA2-70350474.6
7/8"-9UNCA4-80445603.4
1"-8UNCGrade 2395535.6
1"-8UNCGrade 5615833.9
1"-8UNCGrade 88651173.0
1"-8UNCA2-70540732.2
1"-8UNCA4-80680922.0
No rows match your search. Try a different term or filter.

When NOT to Use Calculated Torque

  • Engine head bolts and connecting rod bolts have their own specs. Always follow the engine maker's values.
  • Flanged joints with gaskets need torque that accounts for gasket crush. Use the flange standard, not this calculator.
  • Structural steel connections follow AISC or RCSC specs. These joints use turn-of-nut or tension-control methods.
  • Torque-to-yield (TTY) bolts stretch on purpose. They cannot be reused or torqued with standard methods.
  • Bolts in high-temperature service need adjusted values. Heat changes friction and bolt strength.
  • If the joint has a specific torque sequence (like a star pattern), always follow that sequence.
  • These values are for guidance only. For safety-critical work, verify with a qualified engineer.

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Frequently Asked Questions

What is the torque formula for bolts?

The basic formula is T = K × D × P. T is torque. K is the friction factor. D is the bolt diameter. P is the clamp load. The clamp load is 75% of the bolt's proof load. This gives you a safe starting point for most bolted joints.

How does lubrication affect bolt torque?

Lubrication cuts friction on the threads and under the bolt head. Less friction means more of your torque turns into clamping force. A dry bolt needs more torque than an oiled bolt to get the same clamp load. Always match your torque value to the actual surface. If you oil a bolt but use a dry torque value, you may over-tighten it.

What is the difference between Grade 5 and Grade 8 bolts?

Grade 5 bolts have a proof load of about 85,000 psi. Grade 8 bolts are stronger at about 120,000 psi. Grade 8 bolts hold more force before they stretch or break. Use Grade 5 for most jobs. Use Grade 8 when you need extra strength, like heavy equipment or high-stress joints.

Can I use this calculator for critical joints like head bolts or flanges?

No. This tool gives general torque values. Critical joints like engine head bolts, pressure vessel flanges, and structural connections have their own specs. Those specs account for gasket crush, joint relaxation, and tightening order. Always follow the maker's torque values for critical work.

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