Pounds to Newtons Converter
Convert pounds-force to newtons (lbf to N) for physics, weight and ratings
1 pound-force = 4.448222 newtons. To convert lbf to N, multiply the pounds by 4.44822, so 150 lbf is 667.23 N.
How to convert pounds to newtons
A pound-force is defined as the force that standard gravity (9.80665 m/s²) exerts on a mass of exactly 0.45359237 kg. By Newton's second law, F = m × a, so 1 lbf = 0.45359237 kg × 9.80665 m/s² = 4.4482216152605 N. Because both numbers are exact by definition, so is the factor. The newtons to pounds converter divides by the same number, and the force converter covers kgf, kN and dynes as well.
When a problem gives a mass in pounds and asks for a weight in newtons, the answer is the same number: a 150 lb mass weighs 150 lbf at standard gravity, which is 667.23 N. The trap is using a rounded g. Textbooks that take g = 9.8 or 9.81 get slightly different answers, shown below. For mass alone, convert with the lbs to kg converter.
Step by step
- Take the force (or mass weighed at standard gravity) in pounds.
- Multiply by 4.44822.
- Divide by 1,000 if you want kilonewtons.
- Round to the precision the problem or spec needs.
See it on a scale
Worked examples
A 10 lb bag of flour on a scale, an adult's body weight and a common off-road winch rating.
10 lbf × 4.448221615 = 44.482216 N
= 44.482216 N
150 lbf × 4.448221615 = 667.23324 N
= 667.23324 N
9,500 lbf × 4.448221615 = 42,258.105 N
= 42,258.105 N
How many newtons is a kip?
One kip, short for kilopound-force, is 1,000 lbf, which is 4,448.2216 N or about 4.448 kN. US structural and civil engineers use it for beam loads, column capacities and bolt forces, and ksi (kips per square inch) for stress. The unit keeps structural numbers short: a 25,000 lbf column load is simply written as 25 kips.
Converting kips is the same multiplication scaled by a thousand: multiply kips by 4.44822 to get kilonewtons.
| Load | Kilonewtons | Tonnes-force |
|---|---|---|
| 1 kip | 4.448 kN | 0.454 tf |
| 10 kips | 44.482 kN | 4.536 tf |
| 50 kips | 222.411 kN | 22.68 tf |
| 100 kips | 444.822 kN | 45.359 tf |
Stress converts the same way: 1 ksi is 6.895 MPa, because 1 psi is 6.895 kPa. A metric structural drawing would show the loads above in kN and the stresses in MPa. When you convert catalog values, compare like with like: allowable loads with allowable loads, and ultimate capacities with ultimate capacities.
How many newtons is a pound of thrust?
One pound of thrust is one pound-force, 4.448 N, so multiply thrust in lbf by 4.44822 for newtons or by 0.00444822 for kilonewtons. US engine makers quote thrust in pounds, while European and many international sources quote kN.
| Thrust rating | Newtons | Kilonewtons |
|---|---|---|
| 1,000 lbf | 4,448 N | 4.45 kN |
| 30,000 lbf | 133,447 N | 133.45 kN |
| 100,000 lbf | 444,822 N | 444.82 kN |
Rocket stages rated in millions of pounds move into meganewtons: 1,000,000 lbf is 4.448 MN. Thrust is a force at the engine mounts, so the conversion is direct, with no mass or gravity step. A thrust-to-weight ratio compares that force with the vehicle's weight, so put both figures in the same unit, pounds-force or newtons, before you divide. Jet engine thrust also changes with altitude, airspeed and air temperature, so compare published ratings measured under the same conditions, usually static thrust at sea level.
Pounds to newtons conversion chart
Pounds-force from half a pound to 10,000 lbf, with results rounded to three decimals. For larger loads, the kN column in the thrust table below is easier to read.
| Pounds-force (lbf) | Newtons (N) |
|---|---|
| 0.5 lbf | 2.224 N |
| 1 lbf | 4.448 N |
| 2 lbf | 8.896 N |
| 3 lbf | 13.345 N |
| 4 lbf | 17.793 N |
| 5 lbf | 22.241 N |
| 10 lbf | 44.482 N |
| 15 lbf | 66.723 N |
| 20 lbf | 88.964 N |
| 25 lbf | 111.206 N |
| 30 lbf | 133.447 N |
| 40 lbf | 177.929 N |
| 50 lbf | 222.411 N |
| 75 lbf | 333.617 N |
| 100 lbf | 444.822 N |
| 125 lbf | 556.028 N |
| 150 lbf | 667.233 N |
| 175 lbf | 778.439 N |
| 200 lbf | 889.644 N |
| 250 lbf | 1,112.055 N |
| 300 lbf | 1,334.466 N |
| 400 lbf | 1,779.289 N |
| 500 lbf | 2,224.111 N |
| 750 lbf | 3,336.166 N |
| 1,000 lbf | 4,448.222 N |
| 2,000 lbf | 8,896.443 N |
| 5,000 lbf | 22,241.108 N |
| 10,000 lbf | 44,482.216 N |
Pounds-force vs newtons: which unit is bigger?
The pound-force is the bigger unit, about four and a half newtons, and the two belong to different measurement systems.
| Attribute | Pounds-force | Newtons |
|---|---|---|
| Symbol | lbf | N |
| System | Imperial / US | SI derived unit |
| Defined as | 4.4482216152605 N | 1 kg·m/s² |
| One unit equals | 4.4482216 N | 0.22480894 lbf |
| Thousand-unit multiple | Kip (kilopound-force) = 1,000 lbf | Kilonewton (kN) = 1,000 N |
| Coherent mass and acceleration | Slug and ft/s² | Kilogram and m/s² |
| Weight it represents at standard gravity | A 1 lb mass (453.6 g) | About 102 g of mass |
| Typical rating language | lb on winches, drawer slides and archery draw weights | N or kN on gas struts, carabiners and load cells |
4 key differences
- Converting pounds-force to newtons multiplies the figure by 4.448, so a 100 lbf rating becomes 444.8 N.
- US structural drawings express large loads in kips, while metric drawings show the same loads in kilonewtons.
- The slug, about 14.594 kg, is the mass that 1 lbf accelerates at 1 ft/s², the counterpart of the kilogram for the newton.
- A newton rating can only ever describe a force, whereas a figure in pounds may be a force or a mass depending on context.
How much do you weigh in newtons?
Multiply your weight in pounds by 4.44822: at standard gravity a 120 lb person weighs 533.79 N and a 180 lb person weighs 800.68 N. The table shows weight as a force, with the mass in kilograms for reference; this is the figure physics problems want when they ask for weight in newtons.
| Weight | Mass | Force | Kilonewtons |
|---|---|---|---|
| 50 lb | 22.68 kg | 222.41 N | 0.2224 kN |
| 100 lb | 45.36 kg | 444.82 N | 0.4448 kN |
| 120 lb | 54.43 kg | 533.79 N | 0.5338 kN |
| 140 lb | 63.5 kg | 622.75 N | 0.6228 kN |
| 150 lb | 68.04 kg | 667.23 N | 0.6672 kN |
| 160 lb | 72.57 kg | 711.72 N | 0.7117 kN |
| 180 lb | 81.65 kg | 800.68 N | 0.8007 kN |
| 200 lb | 90.72 kg | 889.64 N | 0.8896 kN |
| 220 lb | 99.79 kg | 978.61 N | 0.9786 kN |
| 250 lb | 113.4 kg | 1,112.06 N | 1.1121 kN |
| 300 lb | 136.08 kg | 1,334.47 N | 1.3345 kN |
Why does my textbook give a different answer in newtons?
Usually because the book rounds standard gravity: with g = 9.8 m/s² a 150 lb person weighs 666.78 N, with 9.81 it is 667.46 N, and the exact figure is 667.23 N. The differences are under 0.07%, so use the g your course specifies and do not be alarmed if an answer key disagrees in the last digit.
Older US engineering texts use the slug as the mass unit, defined so that 1 lbf accelerates 1 slug at 1 ft/s². One slug is 14.5939 kg, about 32.174 lb, and standard gravity in feet is 32.174 ft/s². In that system, a 150 lbf weight corresponds to a mass of 4.662 slugs.
Force, not pressure or torque
Pounds per square inch (psi) is pressure, force per area, and pound-feet is torque, force times distance. Neither converts to newtons directly. Use the psi to kPa converter or the ft-lbs to Nm converter instead.
Winch, towing and thrust ratings: lbf to kN
Winches, hoists, recovery straps and jet engines in the US are rated in pounds (meaning pounds-force), while European specs use kN or tonnes-force (tf). This table converts common rating values.
| Rating | Newtons | Kilonewtons | Tonnes-force |
|---|---|---|---|
| 500 lbf | 2,224 N | 2.22 kN | 0.227 tf |
| 1,000 lbf | 4,448 N | 4.45 kN | 0.454 tf |
| 2,000 lbf | 8,896 N | 8.9 kN | 0.907 tf |
| 5,000 lbf | 22,241 N | 22.24 kN | 2.268 tf |
| 8,000 lbf | 35,586 N | 35.59 kN | 3.629 tf |
| 9,500 lbf | 42,258 N | 42.26 kN | 4.309 tf |
| 12,000 lbf | 53,379 N | 53.38 kN | 5.443 tf |
| 20,000 lbf | 88,964 N | 88.96 kN | 9.072 tf |
| 50,000 lbf | 222,411 N | 222.41 kN | 22.68 tf |
| 100,000 lbf | 444,822 N | 444.82 kN | 45.359 tf |
What does a pound rating mean on a US spec sheet?
It almost always means pounds-force, so multiply the rating by 4.44822 to compare it with a newton or kilonewton figure from Europe or Asia. Most US product ratings that say "lb" for a pull, push or load work this way:
- Winches: a 9,500 lb winch is rated for 42.3 kN of line pull on the first layer of rope. Pull drops on outer layers.
- Drawer slides and shelf brackets: a 100 lb slide rating is 445 N.
- Fastener and anchor pull-out values: a 1,000 lbf rating is 4.45 kN.
- Archery: a 50 lb draw weight is 222 N at full draw.
Working load limits are always well below breaking strength. Convert the published working load, and follow the manufacturer's safety factors and instructions.
What mistakes do people make converting pounds to newtons?
The classic slips are multiplying by 0.4536, which gives kilograms rather than newtons, multiplying by 9.81 without converting to kilograms first, and treating psi as if it were a force.
- Converting to kilograms by mistake. Multiplying by 0.4536 gives mass in kg, not force. 150 lb is 68.04 kg of mass but 667.2 N of force.
- Multiplying by 9.81 without converting to kg first. 150 × 9.81 = 1,471.5, which is meaningless as a force in newtons.
- Mixing lbf and psi. A 30 psi reading is a pressure; you need the area to get a force.
For a quick estimate that avoids them, multiply by 4.5 and take off 1%. For 200 lbf: 200 × 4.5 = 900, minus 9 = 891 N, close to the exact 889.6 N. With a calculator handy, multiplying by 4.45 is within 0.04%.
Older metric specs in kilogram-force are covered by the kgf to newtons converter, and every force unit is on the force converter.
Sources and further reading
The standards and references behind the numbers on this page. Links open in a new tab.
Standards and official sources
Further reading
- Pound-forceWikipedia
- NewtonWikipedia
Pounds to newtons FAQs
Short, exact answers to what people ask most.
How many newtons is 1 pound?
One pound-force equals exactly 4.4482216152605 N, about 4.448 N.
What is 10 lbs in newtons?
10 lbf is 44.48 N. A 10 lb mass weighs the same 44.48 N at standard gravity.
What is 100 lbs in newtons?
100 lbf equals 444.82 N, or about 0.445 kN.
How many newtons does a 150 lb person weigh?
A 150 lb person weighs 667.23 N at standard gravity. Their mass is 68.04 kg.
Is lbs the same as lbf?
Not strictly. lb is a unit of mass and lbf is a unit of force, but at standard gravity a 1 lb mass weighs exactly 1 lbf, so everyday usage treats them as the same number.
Why is 1 lbf equal to 4.448 newtons?
Because 1 lbf is the weight of 0.45359237 kg at standard gravity, and 0.45359237 × 9.80665 = 4.4482216152605 N.
What is 50 lbs in newtons?
50 lbf is 222.41 N, and a 50 lb mass weighs the same 222.41 N at standard gravity.
How many kN is 10,000 lbf?
10,000 lbf equals 44.48 kN, which is also 10 kips.
Related conversions
Factors from NIST SP 811 (2008), Appendix B, for the pound-force, kip and slug; standard gravity 9.80665 m/s² from the 3rd CGPM (1901); the pound as 0.45359237 kg under the 1959 International Yard and Pound Agreement. Last updated . How we verify our numbers.