How is force measured when tightening bolts using a torque wrench?

• A. Pound-inch
• B. Newton meter
• C. Kilogram
• D. Joule

Answer: (B)

Tightening a bolt with a torque wrench measures torque—the rotational effect of the tightening force, not the raw force itself. Torque is the product of the applied force and the distance from the bolt center (the lever arm). In the SI system, this rotational measure is expressed in newton-meters (N·m). That unit directly reflects how hard and how far you’re turning the bolt, which is exactly what the wrench is calibrated to measure and control.

Pound-inch is also a torque unit used in some regions, but the standard SI unit used in most technical contexts is newton-meters. Kilogram is a mass unit, not a torque unit, and joule is energy, not torque. Some torque wrenches can display other units like ft·lb or in·lb, depending on settings, but the primary and most widely used unit for torque is newton-meters.