K = constant that depends on the bolt material and size
d = nominal bolt diameter (m, ft)
F = axial bolt force (N, lbf)
l = lubrication factor (%)
Typical values for K with mild-steel bolts in range 1/4" to 1":
Note! - be aware that this is a rough calculation where the screw pitch is not included. Typical Metric and Imperial bolt torques are indicated in the links below:
Manufacturing data should always be checked before use.
In addition the accuracy of a torque wrench is normally no better than +-25%.
Typical metric and imperial bolyt torques
The calculator below can be used to calculate the torque required to achieve a given axial bolt force or load. The calculator is generic an can used for imperial and metric units as long as the use of units are consistent.
Note that standard dry torques are normally calculated to produce a tensile stress - or axial force or clamp load - in the bolt that equals to 70% of minimum tensile strength or 75% of proof strength.
The required bolt clamping force for a joint is 20000 lbs. The torque required for a 3/4" dry steel bolt with 0% lubrication to achieve this tension can be calculated as
Tdry = (0.2) (20000 lb) (0.75 in) (1/12 ft/in) (1 - (0%) / (100%))
= 250 (lbf ft)
The proof load for a M30 metric bolt grad 8.8 is 337000 N. The torque required to achieve this tension with a dry bolt with 0% lubrication can be calculated as
Tdry = (0.2) (337000 N) (30 mm) (10-3 m/mm)
= 2022 (Nm)
Lubricating the bolt with SAE 30 oil reduces the torque required to achieve the same tension with approximately 40%. The reduced torque can be calculated
TSAE30 = (2022 Nm) (1 - (40%) / (100%))
= 1213 Nm
Eq. 1 can be rearranged to express bolt force as
F = T / (K d (1 - l / 100)) (1a)
The proof load for a M30 metric bolt grad 8.8 is 337000 N. The torque required to achieve this force with a dry bolt is calculated to 2022 Nm.
By failure the bolt is lubricated and tightened with the same torque 2022 Nm. The force acting in the lubricated bolt can be calculated as
Flubricated = (2022 Nm) / (0.2 (0.03 m) (1 - (40%) / (100%)))
= 561667 N
This is way above what the bolt can handle and fatal failure is likely.
This calculator can be used to calculate the force acting in a bolt.
Bolts, nuts and threaded rods - torque, tension and loads.
Tensile stress and Hooke's Law.
Improvise a torque wrench with a luggage scale.
Minimum ultimate tensile and proof loads for metric bolts with coarse or fine threads.
Recommended thightening torque metric bolts.
Proof loads of metric nuts - coarse and fine threads.
Lubrication effect on bolt tension and torque.
Threaded bolts tensile stress area.
Weight rating of threaded hanger rods.
Proof load capacities of metric threaded steel rods.
Tensile strength and proof loads SAE bolts.
Recommended bolt torques.
ANSI/ASME B18.2.1 Dimensions of Hex Bolts - Imperial units.
ANSI/ASME B18.2.3M Dimensions of Hex Bolts - Metric units.
Torque specifications Whitworth bolts.
Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!
We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.
Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.