Foot-pound to Inch-Ounce
ft-lb
in-oz
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
| No conversion history to show. | ||
Quick Reference Table (Foot-pound to Inch-Ounce)
| Foot-pound (ft-lb) | Inch-Ounce (in-oz) |
|---|---|
| 1 | 192.00000000000002039212 |
| 12 | 2,304.00000000000024470542 |
| 50 | 9,600.00000000000101960592 |
| 100 | 19,200.00000000000203921183 |
| 200 | 38,400.00000000000407842366 |
| 400 | 76,800.00000000000815684732 |
| 600 | 115,200.00000000001223527098 |
About Foot-pound (ft-lb)
The foot-pound (ft·lb) is the standard unit of torque and mechanical energy in the US customary system, equal to approximately 1.35582 joules. It represents the work done by a force of one pound-force through a displacement of one foot. Engine torque in American automotive engineering is quoted exclusively in foot-pounds (e.g., a V8 pickup truck producing 400 ft·lb). Bolt torque specifications in the US use foot-pounds for larger fasteners. One foot-pound equals 12 inch-pounds.
A typical car engine produces 150–400 ft·lb of torque. A cylinder head bolt on an engine is typically torqued to 60–90 ft·lb.
About Inch-Ounce (in-oz)
The inch-ounce (in·oz) is a unit of very small torque equal to approximately 0.007062 joules — 1/16 of an inch-pound. It is used for servo motor torque ratings in model aircraft and small robotics, miniature instrument spring tensions, and the adjustment of precision optical and scientific instruments. Where inch-pounds are too coarse for the application, inch-ounces provide a finer unit without switching to SI.
A small servo motor for a model aircraft may be rated at 40–80 in·oz of torque. A clock escapement spring tension is typically a few in·oz.
Foot-pound – Frequently Asked Questions
Why is engine torque measured in foot-pounds in the US?
American automotive engineering adopted foot-pounds because it was the natural imperial torque unit — one pound-force at one foot from the crankshaft center. The convention became entrenched through SAE standards, shop manuals, and dyno testing. Converting to newton-meters (1 ft·lb ≈ 1.3558 N·m) is straightforward, but the entire US aftermarket ecosystem — torque wrenches, spec sheets, and mechanics' training — runs on foot-pounds.
Why do diesel engines produce more torque but less horsepower than petrol engines at the same displacement?
Diesel engines compress air to much higher ratios (15–22:1 vs 8–12:1 for petrol), creating higher cylinder pressures that push harder on the piston — more force per stroke means more torque. But diesels rev lower (typically 4,000–4,500 RPM max vs 6,000–8,000 RPM) because the heavier rotating assembly and slower combustion limit speed. Since horsepower = torque × RPM / 5,252, the lower RPM ceiling caps peak horsepower despite the torque advantage.
What is the torque-to-horsepower relationship and why does it cross at 5,252 RPM?
Horsepower = torque (ft·lb) × RPM / 5,252. The constant 5,252 comes from unit conversion: 1 HP = 33,000 ft·lb/min, and 33,000 / (2π) ≈ 5,252. This means torque and horsepower curves on a dyno chart always intersect at exactly 5,252 RPM. Below that speed, torque is numerically higher; above it, horsepower is. This is why trucks optimize for low-RPM torque (pulling force) while sportscars chase high-RPM horsepower (speed).
What foot-pound torque values are typical for car lug nuts?
Most passenger cars specify 80–100 ft·lb for wheel lug nuts; light trucks and SUVs call for 100–140 ft·lb; and heavy-duty trucks may require 450–500 ft·lb. Under-torquing risks the wheel coming loose, while over-torquing can warp brake rotors or snap studs. A calibrated torque wrench — not an impact gun alone — is the safe approach.
How does foot-pound muzzle energy relate to firearm stopping power?
Muzzle energy in foot-pounds measures the kinetic energy of a bullet leaving the barrel. A 9 mm pistol produces about 350–400 ft·lb, a .45 ACP about 350–500 ft·lb, and a .308 rifle about 2,600–2,800 ft·lb. While muzzle energy is one factor in terminal performance, bullet construction, sectional density, and shot placement matter at least as much in real-world ballistics.
Inch-Ounce – Frequently Asked Questions
What are inch-ounces used for in hobby servos and RC models?
RC servo motors are rated by torque in inch-ounces (or oz·in) because the forces involved are tiny. A standard micro servo produces 40–60 in·oz, which is enough to deflect a model aircraft aileron. High-torque digital servos for 1/10-scale RC cars reach 200–400 in·oz. The inch-ounce scale gives hobbyists whole-number specs that are easy to compare.
Why do high-end RC servos specify torque at different voltages (4.8V vs 6V)?
Servo motors produce more torque at higher voltage because the motor windings draw more current and generate a stronger magnetic field. A servo rated at 60 in·oz at 4.8 V might deliver 75 in·oz at 6 V — a 25% boost. RC pilots choose voltage based on the tradeoff: 6 V gives snappier response and more holding torque for aerobatics, but draws more current and generates more heat, reducing servo lifespan. Competition flyers often run 7.4 V for maximum performance, accepting shorter gear life.
Why use inch-ounces instead of newton-meters for small torque values?
Inch-ounces give convenient whole numbers for very small torques where newton-meters would be awkward decimals (e.g., 50 in·oz ≈ 0.353 N·m). The RC hobby, miniature clockwork, and precision instrument industries in the US developed around imperial units, and the convention persists even as SI gains ground. Many datasheets now list both units side by side.
What torque in inch-ounces does a clock or watch mechanism require?
A mechanical wristwatch mainspring delivers roughly 2–5 in·oz of torque. Larger mantel clocks may have mainspring torques of 10–30 in·oz. Escapement adjustments are even finer, sometimes below 1 in·oz. Horologists use inch-ounces (or gram-centimeters) because these scales match the delicate forces in timekeeping mechanisms.
How does inch-ounce torque relate to servo motor performance in robotics?
A servo's inch-ounce rating tells you the maximum force it can exert at one inch from the output shaft. A 100 in·oz servo can hold 100 ounces (6.25 lb) at 1 inch, or 50 ounces at 2 inches. Robotics designers use this to size servos for joint loads — a small robotic arm lifting 1 lb at 4 inches needs at least 64 in·oz, plus a safety margin of 50% or more.