Torque Wrench Extension Calculator
Adjust wrench setting when using an extension.
Results update as you type.
How it works
Adding an extension or crowfoot adapter in line with a torque wrench changes how much torque actually reaches the fastener, and this calculator finds the setting you should dial in to hit your target. You enter the desired torque at the fastener, the wrench length from the drive pivot to where you grip, and the length of the extension, and it returns the corrected wrench setting. The reason a correction is needed is leverage: an in-line extension lengthens the effective lever arm, so for a given wrench reading the fastener sees more torque. To compensate, you set the wrench lower than the target, in proportion to the wrench length divided by the total combined length. For example, a 12-inch wrench with a 3-inch extension needs to be set to 80 lb-ft to deliver 100 lb-ft at the fastener. Getting this right matters because over- or under-torquing fasteners can cause failures, leaks, or stripped threads. Two important notes: this applies only when the extension is in line (extending the length), not when a socket extension simply goes deeper along the drive axis, which does not change torque; and if the adapter is mounted at an angle, a different correction applies. Enter the desired torque, wrench length, and extension length to find the setting.
Setting = desired torque × wrench length ÷ (wrench length + extension)
When an extension is added in line with the wrench, it lengthens the effective lever, so the fastener receives more torque than the wrench reads. Multiplying the desired torque by the wrench length divided by the combined wrench-plus-extension length gives the lower setting to dial into the wrench.
Source:Torque leverage mechanics
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter desired torque at fastener, wrench length (pivot to handle) and extension length.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Wrench setting to dial in updates instantly as you type — no button to press.
Frequently asked questions
Why does an extension change torque wrench readings?
An in-line extension lengthens the effective lever from the wrench's drive to the fastener. Since torque equals force times lever length, the same handle force produces more torque at the fastener than the wrench indicates. To deliver the correct torque, you must set the wrench lower to account for the added leverage the extension provides.
How do I calculate the corrected setting?
Multiply your desired torque by the wrench length, then divide by the sum of the wrench length and the extension length. This gives a lower number to dial into the wrench. For a 12-inch wrench with a 3-inch extension targeting 100 lb-ft, the setting is 80 lb-ft, which the calculator computes for you.
Does a regular socket extension need this correction?
No. A standard socket extension that goes deeper along the drive axis, in line with the socket rather than lengthening the wrench's lever, does not change the torque delivered. The correction only applies to adapters like crowfoot or offset attachments that extend the effective length of the wrench in the direction of the handle.
What if the adapter is at an angle?
If a crowfoot or adapter is mounted at an angle to the wrench rather than straight in line, the effective length change depends on the angle, and a different formula using the cosine of the angle applies. This calculator assumes the extension is in line with the wrench. For angled setups, consult the specific geometry or mount it at 90 degrees to neutralize the effect.
Why is correct torque important?
Fasteners are engineered to be tightened to a specific torque. Over-torquing can stretch or snap bolts, strip threads, or crush gaskets, while under-torquing can let parts loosen, leak, or fail. Using an extension without correcting the setting throws off the applied torque, so calculating the right wrench setting keeps critical fasteners within their proper specification.