Torque Wrench Extension Calculator
Calculate the corrected torque wrench setting when using an extension or crow's foot adapter.
Enter torque spec and extension length for the safe reading.
A torque wrench applies a specific rotational force (torque) to a fastener to prevent under-tightening (which causes loosening) or over-tightening (which strips threads or breaks bolts). Torque is measured in Newton-meters (N·m) or foot-pounds (ft·lb).
Formula: Torque = Force × Lever Arm Length T = F × L
Unit conversions:
- 1 ft·lb = 1.35582 N·m
- 1 N·m = 0.73756 ft·lb
- 1 in·lb = 0.11298 N·m
Extension correction formula (when using a torque wrench extension): Actual Torque at Fastener = Wrench Setting × (L + E) ÷ L
- L = effective length of the torque wrench (pivot to head)
- E = extension length
Rearranged to find the wrench setting needed: Wrench Setting = Desired Torque × L ÷ (L + E)
What each variable means:
- Torque (T) — rotational force in N·m or ft·lb.
- Force (F) — applied force in Newtons or pounds.
- Lever Arm (L) — distance from pivot point to where force is applied.
- Extension (E) — additional length added to the wrench head.
Worked example — extension correction: You need 100 ft·lb at the fastener. Wrench is 18 inches long; extension adds 4 inches.
Wrench Setting = 100 × 18 ÷ (18 + 4) = 100 × 18 ÷ 22 = 81.8 ft·lb
Common torque specifications:
- Lug nuts (most passenger cars): 80–120 ft·lb
- Spark plugs: 15–25 ft·lb
- Oil drain plug: 25–35 ft·lb
- Cylinder head bolts: 60–80 ft·lb (check OEM spec)
- Wheel bearing nut: 150–185 ft·lb
Always torque in a star pattern for multi-bolt applications.