Bolt Torque to Clamp Load

Short-form torque T = K * D * F with grade proof loads.

Run the calculator

Example

You enter

Grade SAE_5
Diameter (in) 0.5
Lubrication dry
Preload fraction (0-1) 0.75

You get

Clamp load 9046 lb
Torque (in-lb) 904.6
Torque 75.4 ft-lb
Nut factor K for this lubrication 0.2

Details, formula, and sources

T = K × D × F where T is torque (ft-lb), K is the nut factor, D is bolt diameter, F is desired clamp load (= proof load × torque-tension factor). Proof loads per ASTM / SAE bolt-grade specifications.

ASTM A325 / A490 / SAE J429 by name.

ASTM / SAE licensed; principles free in Machinery's Handbook (free at archive.org for older editions).

Estimate. AHJ and licensed structural engineer govern.

Field names used by the API: grade, diameter_in, lubrication, preload_fraction, F_lb, torque_in_lb, torque_ft_lb, K

Nut factor K 0.20 dry / 0.15 lubricated unless user suppliesengineering practice
Proof-load table data/construction/bolt-grades.jsonASTM / SAE by name