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Torque wrench with an extension: what setting gives the right torque?

Correct the torque wrench setting when a crowfoot, adapter or extension lengthens the wrench, so the fastener receives the specified torque.

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Your inputs

Value out of range

Value out of range

Value out of range

°

Value out of range

Results

Setting on the torque wrench

85.7

Set lower than the required torque

Error without correction

16.7%

Torque applied if you set the wrench to the required value
116.7
Effective length
21.0

When the wrench cannot reach

Crowfoot wrenches, offset adapters and torque extensions let you tighten fasteners a socket cannot reach, such as brake lines, fuel fittings or nuts behind a bracket. The catch is that they lengthen the lever arm, so the fastener receives more torque than the wrench shows. Aviation and automotive manuals give the correction for this, and this calculator does it for you.

The formula

With L the effective length of the torque wrench, from the center of the handle grip to the center of the drive, and E the length of the extension, from the drive to the center of the fastener:

Wrench setting = required torque × L ÷ (L + E)

If the adapter is mounted at an angle to the wrench, only the part of the extension along the wrench counts: E × cos(angle). At 90°, the extension adds nothing and no correction is needed. Pointed back toward the handle, at 180°, the extension shortens the lever and the setting must go up.

Example

A fastener needs 100 ft·lb. The wrench measures 18 inches from grip to drive and the crowfoot adds 3 inches in line:

  • Setting: 100 × 18 ÷ (18 + 3) = 85.7 ft·lb
  • Without correction, the fastener would get about 116.7 ft·lb, almost 17% too much.

Tips for accurate torque

  • Measure L from the point where your hand applies force, usually the center of the grip or a mark on the handle.
  • Hold the wrench by the grip, not the end of the handle.
  • Turning the crowfoot 90° to the wrench avoids the correction entirely when there is room to do so.
  • Straight socket extensions along the axis of the bolt need no correction.
  • Flexible joints and long extensions absorb some torque; follow the manufacturer’s instructions for critical joints.

Frequently asked questions

Why does an extension change the torque?

A crowfoot or adapter that sticks out in line with the wrench lengthens the lever arm. The wrench measures the torque at its own drive, but the fastener sees your force times the longer total length, so it gets more torque than the wrench shows.

What is the formula?

Setting = required torque × L ÷ (L + E), where L is the wrench length from the center of the grip to the drive and E the extension length from the drive to the center of the fastener.

What if I turn the adapter at 90°?

Mounted at a right angle to the wrench, the extension adds no length along the lever, so no correction is needed. At other angles, only the part of the extension along the wrench counts, E × cos(angle).

Does a straight socket extension need a correction?

No. An extension bar along the axis of the bolt does not change the lever arm, so the setting stays the same. Only offsets that move the fastener away from the drive need the correction.

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Results are estimates provided for information purposes. They do not replace professional advice.

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