Torque Wrench Extension Calculator
Using a crowfoot or extension changes the effective lever length. Enter the target, wrench length and extension to get the corrected wrench setting.
Last updated: 2026-09-15
How the calculation works
- The wrench reads torque at its own drive; an in-line extension adds lever, so the same setting delivers MORE torque at the bolt.
- The corrected setting scales down by L/(L+E) to land the target at the fastener.
- A 90° crowfoot doesn't change effective length — no correction; an in-line one does.
Formula
T_set = T_target × L / (L + E)
| Symbol | Meaning | Unit |
|---|---|---|
T_set | Corrected wrench setting | N·m |
T_target | Required torque at the fastener | N·m |
L | Wrench effective length | mm |
E | Extension length in line with handle | mm |
Worked example
Interpreting the result
The error direction matters: forgetting the correction always overtightens — broken bolts, stripped threads, warped housings. Measure the wrench length from the drive center (knurled grip midpoint) and the extension from drive to fastener center. Extensions on the drive side (between wrench and socket) don't change anything.
Assumptions
- Extension collinear with the wrench handle (measured center-to-center).
- Rigid extension — flexible joints introduce error regardless of correction.
Limitations
- Universal joints and swivel adapters change the force path — avoid for critical torques.
- 90° crowfoot positions need no correction but check the wrench's own spec for offset loads.
Frequently asked questions
Does a crowfoot change torque?
Only if it extends the effective length in line with the handle. At 90°, no change; in line, apply the correction formula.
Why does my wrench read lower than the bolt gets?
The extension extends the lever: bolt torque = setting × (L+E)/L. Compensate by setting lower — exactly what this calculator computes.