Foot-pounds and inch-pounds are imperial units of torque measuring rotational force. Both represent the twisting force created when a force acts at a distance from an axis of rotation. The distinction lies in the distance unit used: foot-pounds use feet, while inch-pounds use inches. Understanding both units proves essential for mechanical work, automotive repair, and engineering applications where torque specifications vary by fastener size and application.

Converting inch-pounds to foot-pounds requires dividing by 12, reflecting the 12-inch-per-foot relationship. This straightforward conversion enables mechanics and technicians to translate between different torque wrench scales, understand specifications from various sources, and select appropriate tools for specific applications. The simplicity of this conversion makes it one of the easiest torque unit translations in mechanical work.

Understanding inch-pound to foot-pound conversion extends beyond simple mathematics to practical implications affecting tool selection, specification interpretation, and safety outcomes. The choice between these units reflects fastener size, material sensitivity, and precision requirements. Converting accurately ensures proper torque application, prevents component damage, and maintains structural integrity across mechanical, automotive, and precision assembly applications.

Core Conversion Equations

1. How many inch-pounds equal one foot-pound?

Exactly 12 inch-pounds equal 1 foot-pound. This fixed ratio derives from the 12-inch-per-foot length relationship. Since torque equals force times distance, and both units use the same force measurement (pounds), the conversion depends solely on the distance ratio: 12 inches = 1 foot. Therefore, 1 ft-lb = 12 in-lb.

2. How do I convert 180 in-lb to ft-lb?

Divide 180 by 12: 180 ÷ 12 = 15 ft-lb. This represents a common conversion range for small to medium fasteners. The calculation is simple: in-lb divided by 12 always equals ft-lb. For mental math, recognize that any multiple of 12 converts cleanly—120 in-lb = 10 ft-lb, 240 in-lb = 20 ft-lb.

3. Can I use a foot-pound wrench for inch-pound specifications?

Only if the specification converts to a value within your ft-lb wrench's accurate range. Most ft-lb wrenches start at 10-20 ft-lb, making them unsuitable for specs under 120-240 in-lb. Additionally, ft-lb wrenches lack the resolution for low-torque precision work. For specs under 25 ft-lb (300 in-lb), use an inch-pound torque wrench for accuracy and component safety.

4. What happens if I confuse in-lb with ft-lb?

Serious consequences result from unit confusion. Treating 100 in-lb as 100 ft-lb applies 1,200 in-lb (12× over-torque)—stripping threads, breaking bolts, crushing gaskets, damaging components. Treating 100 ft-lb as 100 in-lb applies only 8.3 ft-lb (12× under-torque)—creating loose fasteners, joint separation, and safety hazards. Always verify specification units before torquing.

5. Why do specifications use different torque units?

Unit selection reflects fastener size and required precision. Small, delicate fasteners (electronics, bicycles) use inch-pounds for finer control and higher resolution at low torques. Large, structural fasteners (automotive, machinery) use foot-pounds for convenient numbers and efficient tool operation. The unit choice provides practical, readable values appropriate to the application scale.

6. What's the best torque range for each unit?

Inch-pounds work best from 5-300 in-lb (0.4-25 ft-lb) providing precision for small fasteners. Foot-pounds work best from 10-200 ft-lb (120-2400 in-lb) handling standard to large fasteners efficiently. The overlap range (120-300 in-lb / 10-25 ft-lb) can use either, with inch-pound wrenches offering better precision and foot-pound wrenches providing simpler readings.

7. Do digital torque wrenches display both units?

Many modern digital torque wrenches offer switchable displays showing multiple units including in-lb, ft-lb, and Nm. This eliminates manual conversion and reduces error risk. However, always verify the active display unit before use—pressing the wrong button can change units without obvious indication, leading to the same 12× errors that manual conversion aims to prevent.

8. Is there a quick mental math trick for this conversion?

For in-lb to ft-lb: recognize multiples of 12. Numbers divisible by 12 convert cleanly (120 in-lb = 10 ft-lb). For others, divide by 10 then subtract about 15% as an estimate. For ft-lb to in-lb: multiply by 10, then add 20% for a close approximation. Exact: 15 ft-lb × 12 = 180 in-lb. Estimate: 15 × 10 = 150, plus 20% = 180 in-lb.

9. Should I buy separate wrenches for each unit?

Buy wrenches based on torque range, not units. An inch-pound wrench (typically 20-250 in-lb) handles precision work. A foot-pound wrench (typically 10-150 ft-lb) handles general automotive. Units are interchangeable through conversion, but range determines applicability. Professional mechanics benefit from both ranges to cover all fastener sizes properly. The unit marking is secondary to the torque range coverage.

10. How accurate does this conversion need to be?

The conversion is mathematically exact (factor of 12), so accuracy depends on measurement, not calculation. Torque wrenches typically offer ±3-5% accuracy. Rounding converted values to match your wrench's resolution makes sense—converting 127 in-lb to 10.583 ft-lb is meaningless if your wrench reads to 0.5 ft-lb increments. Round to 10.5 ft-lb for practical application.