Article — Inch-Pounds to Foot-Pounds Calculator
Inch-pounds to foot-pounds: convert torque exactly
One foot-pound equals exactly 12 inch-pounds. To convert inch-pounds to foot-pounds, divide by 12. To go the other way, multiply by 12. The 12:1 ratio inherits directly from the definition of a foot as 12 inches, so the conversion is mathematically exact with no rounding error.
The calculator at the top of this page converts in either direction with adjustable precision. The article below covers what torque is, where each unit dominates in practice, and the mistakes that can damage fasteners when you get the conversion wrong.
What is torque?
Torque is the rotational equivalent of force. It is what tightens a bolt, turns a wheel, or rotates a shaft. Mathematically, torque equals force times the perpendicular distance from the pivot point: τ = F × r. Apply 10 pounds of force at the end of a 1-foot wrench and you have generated 10 ft-lb of torque on the bolt.
The two factors — force and distance — both matter. Doubling the wrench length doubles the torque for the same hand effort. This is why long breaker bars exist: they let you generate large torque values with manageable force.
What is an inch-pound?
An inch-pound is the torque produced by one pound-force applied at one inch from the pivot. It is a small unit suited to precision work. Electronics assembly torque specs often sit in the 2-10 in-lb range. Small-engine spark plugs and lawn-equipment fasteners run 50-200 in-lb. Optical and dental instruments use even smaller values.
Most inch-pound torque wrenches are dial-type or beam-type, with ranges typically capped around 250-500 in-lb. Above that range the wrench arm becomes physically unwieldy, and users switch to foot-pound tools.
What is a foot-pound?
A foot-pound is the torque produced by one pound-force applied at one foot (12 inches) from the pivot. It is the working unit for automotive and heavy industrial fasteners. Lug nuts on a passenger car run 80-100 ft-lb. Cylinder-head bolts on an engine run 40-120 ft-lb. Heavy structural bolts can require 200+ ft-lb.
Foot-pound torque wrenches are typically click-type or digital, with ranges that cover from about 10 ft-lb up to 250+ ft-lb. The click mechanism makes them easier to use without watching a dial, important in tight engine bays where the bolt may be out of sight.
The proper SAE notation distinguishes torque (work) from energy: pound-foot (lb·ft) for torque and foot-pound (ft·lb) for energy/work. In practice almost everyone writes "ft-lb" or "ft-lbs" for both and lets context disambiguate. Engine-spec sheets and torque-wrench labels almost universally use ft-lb for the torque sense.
The inch-pounds to foot-pounds formula
Divide inch-pounds by 12 to get foot-pounds. Multiply foot-pounds by 12 to get inch-pounds.
in-lb ÷ 12 = ft-lbft-lb × 12 = in-lbft-lb × 1.3558 = N·min-lb × 0.1130 = N·mThe 12:1 ratio is exact because the foot is defined as exactly 12 inches. Both units measure the same physical quantity; the only difference is the lever-arm reference. This is unlike most cross-unit conversions, which involve irrational factors. The conversion produces no rounding error at any scale.
Common inch-pounds to foot-pounds conversions
The conversions people search for most frequently, with practical context:
- 6 in-lb = 0.5 ft-lb (small electronics screw)
- 12 in-lb = 1 ft-lb (light fastener)
- 60 in-lb = 5 ft-lb (lawn equipment, small engine)
- 120 in-lb = 10 ft-lb (automotive light fastener)
- 180 in-lb = 15 ft-lb (spark plug, oil drain plug)
- 240 in-lb = 20 ft-lb (brake hardware, suspension)
- 480 in-lb = 40 ft-lb (structural fastener)
- 960 in-lb = 80 ft-lb (lug nut, passenger car)
Torque by fastener type
Fastener torque specs depend on bolt size, grade, and lubrication. The SAE bolt-torque table below shows typical Grade 5 (medium-strength) dry-installation values.
For typical passenger-car work, foot-pounds dominate. A spark plug torques to 15-20 ft-lb. An oil drain plug to 25-30 ft-lb. Lug nuts to 80-100 ft-lb. Cylinder-head bolts vary from 40 to 120 ft-lb depending on engine.
For small-engine work — chainsaws, lawn equipment, motorcycles — specs more often appear in inch-pounds. Carburetor bolts, magneto plates, valve covers all run in the 30-250 in-lb range. Many small-engine service manuals use both units to avoid confusion.
Published torque specs assume a specific bolt condition: usually dry, plain threads. Lubricated threads need 15-25% less torque to reach the same clamping force. Using a dry-spec value on a lubed bolt over-tightens. Using a wet-spec on a dry bolt under-tightens.
Inch-pounds vs. foot-pounds wrench tips
Choose the wrench rated for your torque range, not a wrench you have to convert toward. A 250 in-lb wrench reads accurately at 100-200 in-lb (around 8-17 ft-lb). A 250 ft-lb wrench reads accurately at 100-200 ft-lb (around 1200-2400 in-lb). The two tools cover different ranges and trying to bridge them mentally invites error.
Torque wrenches read most accurately in the middle 60% of their range. A 50-250 ft-lb wrench is most accurate at 80-200 ft-lb. Pegging the wrench at its minimum or maximum setting reduces accuracy by 5-10%. If a spec falls near a wrench's lower or upper bound, use a different-range wrench.
Common torque-conversion mistakes
Reading "120" as ft-lb when the spec is in-lb. 120 in-lb is a light-duty fastener torque (10 ft-lb). 120 ft-lb is a heavy structural fastener. A factor-of-12 error can shear bolt heads or damage threads. Always read the unit on the spec sheet.
Using a ft-lb wrench at the low end of its range. A 25-250 ft-lb wrench at 15 ft-lb reads with poor accuracy. For 10-25 ft-lb work, switch to an inch-pound wrench rated for the higher inch-pound equivalents (120-300 in-lb).
Ignoring the calibration date. Torque wrenches drift over time. Professional shops calibrate annually; home users should calibrate every 5,000 cycles or two years of use. An uncalibrated wrench may read 10-20% off, well outside the bolt's safe torque window.
Confusing N·m with ft-lb on a metric wrench. A dual-unit wrench may default to either scale. 100 N·m is about 74 ft-lb; reading the wrong scale produces a 35% error. Always confirm the active unit before applying torque.