Pound-inch (lb·in) is a unit of torque that represents the rotational force applied to an object. It is commonly used in the United States and other countries that use the imperial system of units.

In the pound-inch unit:

    "Pound" (lb) is the unit of force.
    "Inch" (in) is the distance from the axis at which the force is applied.

One pound-inch of torque is the torque created by one pound of force applied at a perpendicular distance of one inch from a pivot point.

The formula to calculate torque (τ) in pound-inches is:
τ = F · d

Where:

τ is the torque,
F is the force in pounds,
d is the distance in inches from the axis at which the force is applied.

Example:

If you apply a force of 10 pounds at the end of a lever that is 5 inches long, the torque would be 50 lb·in (10 lb * 5 in).

Usage:

The pound-inch unit is often used in engineering, particularly in automotive and mechanical engineering, to describe the torque applied to fasteners like screws, bolts, and nuts, as well as the torque produced by engines or motors in various applications. It is especially common in contexts where smaller torques are involved, such as in the assembly of consumer electronics or appliances.

In my experience: If you mix up pound-inches and Newton-meters, the result is usually either stripped threads or loose parts. Never assume the unit—always check the specs before you touch the torque wrench. One careless move and your carefully built assembly is either damaged or unreliable.

When working on sensitive equipment or small assemblies, pound-inches are much more practical than larger units. Most electronic devices and household appliances are assembled with pound-inch settings to avoid overtightening, which is a silent killer in the long run.

Bottom line: Torque is not just about strength; it’s about control and accuracy. If you don’t respect the pound-inch values, you’re just gambling with your work quality. A good technician knows how to set the right torque—every time, every fastener.