Force vs. Torque: Newtons, Pound-Force, and Foot-Pounds Explained
By Convert Calc Editorial Team · Published
Force and torque are separate categories on this site because they measure different things — but their units borrow each other’s names badly enough that people convert between them by accident. “Pound” shows up in pound-force (lbf) and again in foot-pound (ft·lb). The newton (N) and the newton-meter (N·m) differ by three characters. A spec sheet that says “450 N” and one that says “450 N·m” are describing physically different requirements, and no conversion factor connects them.
What each one actually measures
Force is a push or a pull: how hard something is being shoved in a straight line. Its SI unit is the newton, defined in terms of base units as kg·m/s². A load cell rated to 5,000 N, the breaking strength of a chain, the clamping load on a bolt, the weight of a parked car pressing on its tires — all of these are forces.
Torque is the twisting effect a force produces about an axis. It depends on the force and on where that force is applied relative to the axis. As NIST’s SI reference puts it, torque “is the cross product of a position vector and a force vector,” and its SI unit is the newton meter.
The “where” is the part people skip. The standard physics treatment defines torque as the force multiplied by the lever arm — the perpendicular distance from the axis of rotation to the line of action of the force. Pull with 100 N on a wrench handle 0.3 m from the bolt center and you apply 30 N·m. Slide your hand out to 0.6 m and the same 100 N pull now delivers 60 N·m. The force didn’t change. The torque doubled.
That is the whole reason torque units are written as a force unit times a length unit. A newton-meter is one newton applied one meter out; a foot-pound is one pound-force applied one foot out. Read the unit name as the recipe for producing the quantity and it stops looking arbitrary.
Why torque isn’t measured in joules
Multiply newtons by meters and you get kg·m²/s², which is dimensionally identical to the joule. SI still keeps them apart deliberately: NIST’s SI guidance states that although torque has the same dimension as energy, “the joule is never used for expressing torque.” Energy is a scalar; torque is a vector quantity with an axis and a direction of rotation. Tightening a bolt to 190 N·m does not mean 190 joules of work went into it — the work depends on how far the fastener actually turned.
This is worth knowing mainly as a sanity check: if a document hands you torque in joules, or converts between N·m and J, something has gone wrong upstream.
The mix-ups that actually cost people money
Inch-pounds read as foot-pounds. There are 12 inch-pounds in a foot-pound, so a wrench set to 100 in·lb when the spec called for 100 ft·lb is tightening to one-twelfth of the intended load. Small fasteners — valve covers, sensor bodies, bicycle stem bolts — get specified in in·lb because the same numbers would be awkward fractions in ft·lb. Those are the fasteners a misread unit destroys first.
ft-lb, lb-ft, and lbf·ft. All three notations appear in service literature for the same quantity. GM’s own service bulletins write it “lb ft”; NIST style would be lbf·ft; most US torque wrenches are dialed in “ft-lb.” Treat them as spellings of one unit and convert nothing.
Force ratings compared against torque specs. A fastener catalog may list clamp load in lbf while the installation spec is in ft·lb. These are not alternate views of the same number. Converting one into the other requires knowing the geometry — thread pitch, friction, and the effective radius at which the force acts — which is why manufacturers publish the torque figure directly rather than expecting you to derive it.
A worked case from a real service bulletin
In January 2020, GM issued service update N192285970 for the 2020 Chevrolet Silverado 2500 HD, filed with NHTSA, after some trucks left the line with lug nuts not tightened to specification. The stated risk: “this condition may cause the wheel assembly to separate from the vehicle.” The corrective procedure reads:
Using a torque wrench and the appropriate socket, alternately and evenly tighten the 8-wheel nuts to 190 N-m (140 lb ft) in a crisscross pattern.
(Service Update N192285970, hosted on NHTSA)
Check the conversion: 190 × 0.7375621 = 140.1 ft·lb. The bulletin’s dual-unit figure is exactly what the N·m to ft·lb converter returns, which is the normal case — manufacturers print both because the spec is metric and the wrench on the bench often isn’t.
Now note what the 190 N·m does not tell you: the force on the wrench handle. That depends entirely on handle length. On a 0.4 m bar you’d need 475 N (about 107 lbf) at the end of it; on a 0.6 m breaker bar, 317 N (71 lbf). The torque spec is fixed by the fastener. The force is whatever your tool geometry demands to produce it, which is why a long breaker bar reaching the same torque feels so much lighter in the hand than a short ratchet.
Reference tables
Force units (base: newton)
| Unit | Symbol | Equals in newtons | Typical use |
|---|---|---|---|
| Newton | N | 1 | SI standard; load cells, structural analysis |
| Kilonewton | kN | 1,000 | Structural loads, press and crane ratings |
| Pound-force | lbf | 4.448222 | US mechanical and structural specs |
| Kilogram-force | kgf | 9.80665 | Older European and Japanese equipment ratings |
| Ounce-force | ozf | 0.2780139 | Small springs, switch actuation forces |
| Dyne | dyn | 0.00001 | CGS system; surface tension, legacy physics literature |
Torque units (base: newton-meter)
| Unit | Symbol | Equals in N·m | In ft·lb | Typical use |
|---|---|---|---|---|
| Newton-meter | N·m | 1 | 0.737562 | SI standard; most manufacturer torque specs |
| Foot-pound | ft·lb | 1.355818 | 1 | US torque wrenches; lug nuts, suspension, engine work |
| Inch-pound | in·lb | 0.1129848 | 0.083333 | Small fasteners, electronics, bicycle components |
| Kilogram-force meter | kgf·m | 9.80665 | 7.233011 | Older Japanese and European service manuals |
| Newton-centimeter | N·cm | 0.01 | 0.0073756 | Precision instruments, small motors |
Conversion factors come from NIST Special Publication 811, Tables B.8 (force) and B.9 (moment of force), the same reference used throughout this site: https://www.nist.gov/pml/special-publication-811
Two quick approximations worth memorizing: 1 N·m ≈ 0.74 ft·lb, and 1 N·m ≈ 8.85 in·lb. For the force side, 1 lbf ≈ 4.45 N and 1 kgf ≈ 9.81 N.
Frequently Asked Questions
My repair manual gives a bolt spec in N·m but my datasheet lists clamp load in lbf. Can I convert between them?
No. Those are different quantities, and no factor links them on its own. The torque figure is what you set on the wrench; the clamp load is the tension the bolt ends up carrying, which depends on thread geometry and friction conditions that the manufacturer accounted for when publishing the torque spec. Use the torque number as given. If you genuinely need clamp load, it has to come from the fastener manufacturer’s data, not from arithmetic on the torque value.
The spec says 8 N·m and my torque wrench’s lowest setting is 20 ft·lb. What now?
8 N·m is about 5.9 ft·lb — below your wrench’s range, so it can’t be set accurately. Convert to inch-pounds instead: 8 N·m ≈ 71 in·lb, and buy or borrow an inch-pound wrench. Using a foot-pound wrench below its calibrated range gives readings you can’t trust, and small fasteners are the ones most likely to strip.
Why does my Japanese service manual list torque in kgf·m?
Kilogram-force meters were standard in Japanese and European service literature before metrication settled on the newton-meter, and older manuals were never rewritten. Multiply by 9.80665 to get N·m — so a 3.5 kgf·m spec is 34.3 N·m, or about 25.3 ft·lb. Many manuals from the transition period print both, and if yours does, check that the two agree before trusting either.
I’ve seen the same spec written as ft-lb and lb-ft. Are those different?
No. Both refer to one pound-force applied at a one-foot lever arm. The strict SI-style notation is lbf·ft, which makes the force unit explicit, but service manuals and wrench dials use all three forms interchangeably. There’s nothing to convert.
Is a 500 N actuator stronger than a 500 N·m motor?
The question doesn’t have an answer as posed — one produces linear force, the other rotation. To compare them you need the radius at which the motor’s torque is applied. A 500 N·m motor driving a 0.1 m radius drum produces 5,000 N of cable tension; the same motor on a 2 m radius arm produces 250 N at the arm’s tip. The torque rating is fixed; the force it yields is a function of geometry.
Practical takeaway
Before converting anything, check which quantity you’re holding:
- A single unit of force (N, kN, lbf, kgf) means a straight-line push or pull. Convert it within the force family — see newtons to lbf.
- A force unit paired with a length unit (N·m, ft·lb, in·lb, kgf·m) means torque. Convert it within the torque family — see N·m to ft·lb or N·m to in·lb.
- Never convert across the two. If a calculation seems to require it, you’re missing a lever-arm length, and that length has to come from the geometry of the actual part.
And when the spec comes from a manufacturer, use the manufacturer’s number. GM printed 190 N·m and 140 lb ft side by side in that bulletin so no technician would have to do arithmetic at the wheel.