Convert lb·ft to N·m pound-feet ↔ newton metres Free Online Secure
Type a value in pound-feet and read it in newton metres at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert lb·ft to N·m (pound-feet ↔ newton metres)
| lb·ft | N·m |
|---|---|
| 1 | 1.3558179483314004 |
| 2 | 2.7116358966628008 |
| 3 | 4.0674538449942012 |
| 5 | 6.779089741657002 |
| 10 | 13.558179483314004 |
| 20 | 27.116358966628008 |
| 50 | 67.79089741657002 |
| 100 | 135.58179483314004 |
Where these units come from
Torque is a force applied at the end of a lever, so its unit is simply a force multiplied by a length: a newton metre is one newton pushing at one metre from the pivot. The pound-foot is the same idea built from the pound-force and the foot, and it stayed in American and British workshops long after the rest of the toolbox went metric. The curiosity of this quantity is that it has exactly the same dimensions as energy — a newton metre and a joule are built from the same ingredients — yet they are never interchanged. A joule is work done; a newton metre of torque is a twist that may do no work at all, because nothing has turned.
Where you meet them
Every wheel on a car is tightened to a stated torque, and so is almost every bolt that matters: engines, bicycles, scaffolding, aircraft. Engine outputs are quoted as torque alongside power, because torque is what pulls away from a standstill while power is what sustains speed. Electric motors have made the number familiar to people who never owned a torque wrench, since they deliver their full torque from zero.
Questions people ask
Is a newton metre the same as a joule?
Dimensionally yes, physically no, and the distinction matters. Both are a newton times a metre, but in a joule the force and the distance point the same way — something moved — while in torque the force acts at right angles to the arm, and the bolt may not turn at all. By convention torque is always written in newton metres and never in joules, precisely so that the two are not mistaken for one another.
Is a pound-foot the same as a foot-pound?
In practice people use both for the same thing, but the careful convention is to write torque as pound-feet (lb·ft) and energy as foot-pounds (ft·lb). The numbers are identical either way, so a torque figure labelled ft·lb converts exactly as this page shows. It is the quantity that differs, not the arithmetic.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Pound-feet to newton-metres: restoring American classics with a metric wrench
The golden age of the American V8 left behind service manuals that give every torque in pound-feet. Today's restorers in Europe, Australia and Asia work with metric torque wrenches and metric reference books, so every figure from an old Chevrolet, Ford or Dodge manual has to be converted. A cylinder-head bolt tightened to the wrong value can warp a head or blow a gasket, and a wheel nut left loose is far worse. To convert lb·ft to N·m, multiply by 1.3558: 100 lb·ft is 135.6 N·m, 450 lb·ft is 610.1 N·m and 25 lb·ft is 33.9 N·m. The calculator above does it as you type, and the sections below take you through a restoration from the engine to the wheels.
The page gives the rule with worked examples, a profile of each unit, a comparison and many cases from classic-car work, followed by the usual mistakes. The calculation runs in your browser and nothing you type is sent anywhere. For any safety-related fastener, follow the manual for the exact model and year.
How to convert lb·ft to N·m: one factor, 1.3558
Where it comes from
A pound-foot is a force of one pound acting one foot from the axis: 4.448222 N × 0.3048 m = 1.355818 N·m. That is the whole basis of a “convert lb·ft to N·m” calculation: multiply the value in lb·ft by 1.3558. 50 lb·ft gives 67.8 N·m, 200 lb·ft gives 271.2 N·m and 500 lb·ft gives 677.9 N·m. In the opposite direction multiply N·m by 0.7376.
Worked examples
The 1970 Chevelle SS 454 LS6 listed 500 lb·ft, which is 677.9 N·m. A 426 Hemi was rated at 490 lb·ft, 664 N·m. A modern 6.2-litre supercharged V8 gives 650 lb·ft, 881 N·m, and an electric pickup 775 lb·ft, 1,051 N·m.
How exact it is
The factor rests on the definitions of the pound and the foot and carries no hidden rounding. For restoration work 1.36 is accurate to 0.3 per cent, within the tolerance of a click wrench.
A quick sanity test
The figure in N·m is a third larger than the figure in lb·ft. If you ended with a smaller number than you began with, you multiplied by 0.7376 by mistake.
The pound-foot
The unit of the old manuals
The pound-foot, written lb·ft or ft-lb, is the customary American unit of torque. Every factory manual of the muscle-car era uses it, along with inch-pounds for small fasteners.
Where it appears
Classic-car manuals, American brochures, wrenches sold in the United States and parts catalogues.
The newton-metre
The unit of the metric workshop
The newton-metre is the SI unit of torque. Torque wrenches sold in most of the world are marked in N·m, and metric reference books, parts lists and data sheets quote it.
Where it appears
Metric torque wrenches, European and Asian manuals and engineering standards.
lb·ft against N·m
One lb·ft equals 1.356 N·m, so the figure in N·m is a third larger. A torque of 100 lb·ft is 135.6 N·m and 500 lb·ft is 677.9 N·m. They are the same torque; only the unit differs.
The conversion is exact and hides no rounding. The trap is direction: from lb·ft to N·m the number grows.
Where the conversion shows up
Engine assembly
Head bolts on an old V8 are typically tightened to 65 to 95 lb·ft, 88 to 129 N·m, in three steps, intake manifold bolts to 25 to 30 lb·ft, 34 to 41 N·m, and main bearing caps to 65 to 110 lb·ft, 88 to 149 N·m. A “convert lb·ft to N·m” calculation for each stage keeps the assembly safe.
Wheels and brakes
Wheel nuts on a classic car need 70 to 90 lb·ft, 95 to 122 N·m. Caliper bolts take 35 to 80 lb·ft, 47 to 108 N·m. Axle nuts on a solid rear axle ask for 150 to 250 lb·ft, 203 to 339 N·m. Re-check them after the first 50 km.
Reading the engine's specification
An engine listed at 425 lb·ft has 576 N·m, a classic big-block at 500 lb·ft has 678 N·m, and an economy engine of 83 lb·ft, like that of an old compact, only 112.5 N·m. The torque figure shows at a glance how the engine was meant to be used.
The great muscle-car torque numbers
The 1970 LS6 454 gave 500 lb·ft, 678 N·m. The 426 Hemi gave 490 lb·ft, 664 N·m. The 428 Cobra Jet gave 440 lb·ft, 597 N·m. These figures were often "gross" values measured without accessories, which is why a modern "net" number for the same engine is lower.
Torque multipliers
For torques above 600 lb·ft, 813 N·m, mechanics use multipliers with ratios of 4:1 or 5:1. A 150 lb·ft, 203 N·m, input then produces 600 to 750 lb·ft, 813 to 1,017 N·m. The wrench is applied to the input side.
Threads, oil and friction
Factory torque values are for threads in the condition the manual describes, usually clean and lightly oiled. Anti-seize compound can raise bolt tension by 20 to 30 per cent at the same torque, so many manuals ask for a reduction of about 20 per cent. A “convert lb·ft to N·m” calculation does not include that correction.
Torque and horsepower
Horsepower is torque in lb·ft times rpm divided by 5,252. An engine making 500 lb·ft at 3,600 rpm gives 343 hp, 256 kW. In metric terms, 678 N·m at 3,600 rpm times 2π gives the same 256 kW. The two systems agree on power even when they disagree on units.
Rounding for the wrench
When you convert lb·ft to N·m, the result may be 677.9 N·m, but a click wrench cannot be set so finely. Set 680 N·m. If the limit is a maximum, round down; if it is a minimum, round up. Torque specifications describe a range, not a point.
The mental shortcut
To convert lb·ft to N·m in your head, add a third and 1.5 per cent of it. For 150 lb·ft: 150 plus 50 gives 200, plus 3 gives 203, close to 203.4. For 30 lb·ft: 40 plus 0.6 gives 40.6, against 40.7.
Spreadsheet formulas
To convert lb·ft to N·m in a spreadsheet, put the lb·ft values in column A and type =A2*1.355818 in column B. For the reverse, =B2/1.355818. A column with =B2/9.80665 gives kgf·m for Japanese manuals.
Landmarks to memorise
10 lb·ft is 13.6 N·m. 25 lb·ft is 33.9 N·m. 50 lb·ft is 67.8 N·m. 100 lb·ft is 135.6 N·m. 200 lb·ft is 271.2 N·m. 500 lb·ft is 677.9 N·m. 1,000 lb·ft is 1,356 N·m. Use these to convert lb·ft to N·m by eye.
Reference ladder
5 lb·ft is 6.8 N·m. 15 lb·ft is 20.3 N·m. 35 lb·ft is 47.5 N·m. 65 lb·ft is 88.1 N·m. 85 lb·ft is 115.2 N·m. 140 lb·ft is 189.8 N·m. 300 lb·ft is 406.7 N·m. 650 lb·ft is 881.3 N·m. A ladder like this makes checking easy.
Checking by reversing
To check a “convert lb·ft to N·m” calculation result, multiply the answer by 0.7376. If 100 lb·ft became 135.6 N·m, then 135.6 times 0.7376 returns 100. A second test is size: N·m should exceed lb·ft by a third.
Related torque units
One lb·ft is 1.356 N·m, 0.1356 daN·m and 0.1383 kgf·m. A torque of 100 lb·ft is 135.6 N·m, 13.56 daN·m and 13.8 kgf·m. All four describe the same torque.
Gross and net ratings
Before 1972 American makers quoted gross torque and power, measured on a bare engine, and later net figures measured with accessories. A 500 lb·ft gross engine may show 440 to 460 lb·ft net, 597 to 624 N·m. When you convert lb·ft to N·m from an old brochure, expect the real figure to be lower.
A worked example
A restorer in Australia rebuilds a 1969 Mustang. The manual gives main-bearing bolts at 95 lb·ft and connecting-rod nuts at 40 lb·ft. In N·m, 95 × 1.3558 = 128.8 and 40 × 1.3558 = 54.2. Setting the wrench to 95 N·m instead would leave the bearing caps 26 per cent too loose.
Tyre and wheel data
Classic cars also list tyre pressures in psi: 24 to 28 psi, which is 1.7 to 1.9 bar. When you convert torque you will likely convert pressure too. The wheel studs hold with 70 to 90 lb·ft, 95 to 122 N·m, while the tyres hold 165 to 193 kPa.
Transmission and differential
Each “convert lb·ft to N·m” calculation for the drivetrain is separate: the pan bolts of an automatic gearbox take 10 to 15 lb·ft, 14 to 20 N·m, the filler plug of a differential 20 to 30 lb·ft, 27 to 41 N·m, and the driveshaft U-bolts 14 to 20 lb·ft, 19 to 27 N·m. A loose bolt may leak, a tight one may crack the housing.
Suspension components
Leaf-spring U-bolts take 40 to 60 lb·ft, 54 to 81 N·m, shock absorber bolts 50 to 70 lb·ft, 68 to 95 N·m, and ball-joint nuts 40 to 80 lb·ft, 54 to 108 N·m. Safety-critical joints should be checked a second time after a short drive.
Steering and brakes
Steering box mounting bolts need 70 to 90 lb·ft, 95 to 122 N·m, and the pitman-arm nut 150 to 180 lb·ft, 203 to 244 N·m. These parts control the car; a conversion mistake can be fatal, so a second person should check the setting.
Engines for boats
American marine engines are often derived from car blocks. A 454 marine engine makes 405 lb·ft, 549 N·m, and the propeller nut takes 40 to 70 lb·ft, 54 to 95 N·m. Boats built in the United States and used elsewhere carry manuals in lb·ft.
Aircraft engines
A six-cylinder aircraft engine of 300 hp at 2,700 rpm produces 583 lb·ft, 790 N·m. Spark plugs are tightened to 360 to 420 in·lb, 30 to 35 lb·ft, 41 to 47 N·m. Aviation manuals use lb·ft or in·lb, and inspectors keep conversion cards.
Old tractors and trucks
An old farm tractor engine with 150 lb·ft, 203 N·m, will have wheel nuts at 100 to 150 lb·ft, 136 to 203 N·m. Vintage truck restorers need torque wrenches with high ranges, up to 500 lb·ft, 678 N·m.
Foot-pounds of energy
Torque in lb·ft is not energy in ft·lbf. The numbers match, 1 lb·ft being 1.356 N·m and 1 ft·lbf 1.356 J, but torque is a turning effect and energy is work. Engineers use N·m for torque and J for energy, and a “convert lb·ft to N·m” calculation concerns only the first.
Two routes to one answer
You can go from lb·ft to N·m directly with 1.3558, or via in·lb: multiply by 12 and then by 0.11298. If the results disagree, a digit was copied wrongly.
Modern performance cars
A supercharged 6.2-litre V8 makes 650 lb·ft, 881 N·m, a 5.0-litre sports coupé 410 lb·ft, 556 N·m, and a 3.0-litre turbo six 400 lb·ft, 542 N·m. The comparison with European cars is clearest in N·m.
Fastener grades and sizes
American bolts are graded by SAE number. A 1/2-inch grade 8 bolt is tightened to about 90 lb·ft, 122 N·m, and a 3/8-inch one to about 45 lb·ft, 61 N·m. Metric bolts of class 10.9 have their own tables in N·m. Restorers often mix both kinds of bolt on one car, so conversion appears at every step of the work.
Pickups and heavy-duty diesels
A heavy-duty diesel pickup lists 1,075 lb·ft, 1,458 N·m, and an electric pickup 775 lb·ft, 1,051 N·m. Tow ratings of 15 tonnes or more follow from such numbers. Torque figures in lb·ft must be converted for comparison with European vans, which typically give 350 to 500 N·m.
Harley-Davidson and cruisers
A big cruiser engine, 114 cubic inches, makes 119 lb·ft, 161 N·m, at low rpm. The rear axle nut takes 60 to 95 lb·ft, 81 to 129 N·m, and the fork pinch bolts 20 to 35 lb·ft, 27 to 47 N·m. American service manuals give lb·ft throughout.
Small fasteners in inch-pounds
For small bolts, carburettor flanges and electrical terminals, American manuals use inch-pounds: 12 in·lb make 1 lb·ft. A torque of 100 in·lb is 8.33 lb·ft, 11.3 N·m, and 50 in·lb is 5.65 N·m. Mistaking in·lb for lb·ft produces a twelve-fold error.
Spark plugs on old engines
Spark plugs with a 14 mm thread need 10 to 15 lb·ft, 14 to 20 N·m, on a cast-iron head and 10 to 12 lb·ft, 14 to 16 N·m, on an aluminium head. Tapered-seat plugs need only 10 lb·ft, 13.6 N·m. The seat type matters more than the thread size.
The click wrench and its scale
An American click wrench of 10 to 150 lb·ft covers 13.6 to 203 N·m. A metric one of 20 to 200 N·m covers 14.8 to 147.5 lb·ft. Neither is accurate below one fifth of its range. Pick the wrench so the target torque falls in its upper two thirds.
Lengthening the wrench
A pipe slipped over a wrench handle raises torque for the same pull. A pull of 150 lb on 1.5 ft of handle creates 225 lb·ft, 305 N·m. Do not use this trick with a click wrench, which can be damaged. With a plain breaker bar it is the standard way of getting a large torque.
More values for convert lb·ft to N·m
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 lb·ft = 0.135582 N·m
- 0.5 lb·ft = 0.677909 N·m
- 3 lb·ft = 4.06745 N·m
- 4 lb·ft = 5.42327 N·m
- 7 lb·ft = 9.49073 N·m
- 15 lb·ft = 20.3373 N·m
- 20 lb·ft = 27.1164 N·m
- 75 lb·ft = 101.686 N·m
- 200 lb·ft = 271.164 N·m
- 500 lb·ft = 677.909 N·m
- 2,000 lb·ft = 2,711.64 N·m
- 10,000 lb·ft = 13,558.2 N·m
Common slips with a “convert lb·ft to N·m” calculation
Multiplying by 0.7376
From lb·ft to N·m the number grows. If 100 lb·ft became 73.8, you used the factor for the other direction.
Mixing lb·ft and in·lb
One lb·ft is 12 in·lb. Reading 100 in·lb as 100 lb·ft would tighten twelve times too hard. Check the unit on the wrench and in the book.
Using the wrong wrench range
A click wrench is not accurate in the lowest fifth of its scale. For 60 N·m choose a wrench covering 40 to 210 N·m, not one covering 20 to 340.
Short answers
How do I convert lb·ft to N·m?
Multiply the lb·ft figure by 1.3558.
How many N·m is 100 lb·ft?
135.58 N·m.
How many N·m is 500 lb·ft?
677.9 N·m.
How many lb·ft is 1 N·m?
0.7376 lb·ft.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other torque conversions see Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert m² to cm², Convert mph to km/h, Convert mi to nmi, Convert MPG (UK) to L/100km, Convert m³ to mm³. The reverse direction is Convert N·m to lb·ft.
In short, a “convert lb·ft to N·m” calculation comes down to multiplying by 1.3558 and writing the unit beside the answer. Your number is computed locally, with no account and no upload.