Torque Wrench Extension Calculator
When you add an in-line extension between a torque wrench and the fastener, it lengthens the effective lever, so the fastener receives more torque than the wrench dial shows. To hit the torque you actually want, the wrench must be set lower. This calculator works out that corrected setting from your target torque, the wrench length and the extension length. The correction assumes a straight extension in line with the wrench, which is the usual case; an extension at an angle needs different handling.
How to use this tool
- Enter the torque you want at the fastener and its unit.
- Enter the wrench length — from the handle pivot to the centre of the drive.
- Enter the extension length, measured along the same line.
- Read the corrected value to dial on the wrench.
- The result also shows what the fastener would receive if you forgot to correct — always lower your setting, never raise it.
The formula
An in-line extension adds to a torque wrench’s effective lever, so the fastener sees more torque than the dial shows. To hit a target torque, the wrench must be set lower, in proportion to the lever lengths.
setting = target × L ÷ (L + E)- target
- Torque wanted at the fastener
- L
- Wrench lever length (handle pivot to drive)
- E
- Extension length, in line with the wrench
This assumes the extension is straight and in line with the wrench. An extension at an angle changes the geometry and needs a different correction.
Worked examples
Extension in line
- Given
- Want 100 N·m, wrench 300 mm, extension 100 mm
- Result
- Set 75 N·m
setting = 100 × 300/400 = 75 N·m. The extension amplifies torque, so the wrench is set lower.
Short extension
- Given
- Want 50 lb·ft, wrench 18 in, extension 2 in
- Result
- Set 45 lb·ft
50 × 18/20 = 45 lb·ft — a modest correction for a short adapter.
Uncorrected risk
- Given
- Same 100 N·m case, dialled 100
- Result
- Fastener gets ≈ 133 N·m
Forgetting the correction over-torques the fastener by a third, which can strip or snap it.
Frequently asked questions
A torque wrench measures the torque at its own drive, based on force times its lever length. An in-line extension moves the fastener farther from the handle, lengthening the lever, so the same handle force produces more torque at the fastener than the wrench reads. The setting must be lowered to compensate.
For a straight in-line extension that lengthens the lever, you always lower the setting, because the fastener sees more than the dial. You would only raise it in the unusual case of an adapter that shortens the effective lever. When in doubt, this calculator gives the right direction and amount.
Measure the wrench length from the centre of the handle grip (the pivot where you apply force) to the centre of the drive square, and the extension length along the same straight line from the drive to the fastener. Both must be along the line of action for the correction to be exact.
The simple formula assumes the extension is straight and in line with the wrench. If the adapter sits at an angle, only the component along the wrench’s line of action counts, and the geometry is more involved. For angled setups, consult the wrench or adapter manufacturer’s guidance.
No. A normal socket or deep socket keeps the fastener on the wrench’s own axis and does not lengthen the lever, so no correction is needed. The correction applies only to extensions that move the drive point away from the wrench along its length, such as crow-foot and flare-nut adapters.
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