UncorrectedReady
0targetmax
Wrench set to —
Fastener gets —
Torque made clear
Set the right torque when your wrench gets an extension.
A visual calculator for crowfoot wrenches, torque adapters and dog-bone extensions. Enter your measurements, then watch the effective lever arm change.
90° means no correctionL is working lengthE is added reach
First, identify the tool
Select a card to see its ruleWhat kind of extension are you using?
Live calculator
See the correction as you turn the angle.
Measure from drive centre to grip centre for L, and drive centre to fastener centre for E. Keep both in the same length unit.
The orange line is the full effective arm from the grip to the fastener projected onto the handle axis: L + E cos θ. E is drawn along the extension itself.
B · Click simulation
Feel the difference before you tighten.
Play the pull using the live calculator values. Both gauges use the same fastener-torque scale and the target mark never moves.
CorrectedReady
0targetmax
Wrench set to —
Fastener gets —
Press play to see the needle rise and the click land.
C · Angle tour
The angle changes the projection, not the tool’s length.
Watch the correction factor move from maximum correction at 0° to reverse correction at 180°. 90° is the no-correction position.
Tool head rotates from 0° to 180°
0° · factor 0.909
At 90°, cos θ is zero, so the extension contributes no projected length.
E · Measure it right
How to measure L and E.
Torque is force multiplied by perpendicular distance. Centre-to-centre measurements are the reliable ones.
L — wrench effective length
Start at the square-drive centre and end at the hand-grip centre—the handle mark or groove where your palm applies force.
E — extension length
Measure from the square-drive centre to the fastener or jaw centre—not to the outer edge of the crowfoot.
Common trap: overall length
The body can extend beyond the working points. Use the drive and grip centres that define the actual torque arm.
Common mistakes
Small measurement mistakes create big torque errors.
Using overall length for L
End L at the hand-grip centre, where force is applied.
Mixing mm and inches
Convert both lengths to one unit before calculating.
Installing at 90°
A perpendicular crowfoot keeps the effective arm unchanged.
The short version
Three steps to a trustworthy setting.
Measure from centres
Measure L from square-drive centre to hand-grip centre, and E from drive centre to fastener centre.
Choose the angle
Use the centreline angle. A 90° crowfoot is the simple, no-correction position.
Set, then verify
Use the calculated setting and keep it within roughly 20–100% of the wrench range.
Formula
Tset = Ttarget × L ÷ (L + E × cos θ)The reverse mode solves for actual torque.Questions, answered
Torque extension FAQ.
Does a normal socket extension need a torque correction?
No. A plain socket extension runs along the drive axis and does not change the wrench’s lever arm. This calculator is for crowfeet, torque adapters and other extensions that move the fastener centre sideways.
Why is 90° the no-correction position?
The extension contributes E × cos θ. At 90°, cos 90° is zero, so the effective lever arm is simply L.
Where exactly should I measure L?
Measure from the square-drive centre to the centre of your hand grip. The outside body length is not the working length.
Where exactly should I measure E?
Measure from the drive centre to the centre of the fastener or nut.
What does a negative correction mean?
Below 90°, a forward extension increases leverage and the wrench setting must be lower. At 180°, it subtracts leverage and the setting becomes higher.
What if the calculated value is outside my wrench range?
Do not force a wrench outside its rated range. Use the optional range check and choose a suitable tool if needed.
Try a known case
Worked examples.
Load an example, then change one value to see what moves.