Lbs to Newtons Converter
Convert pounds (pound-force, lbf) to newtons and newtons back to pounds, with kilonewtons and kilogram-force alongside. Works for weights in pounds as well as force ratings like gas struts, fishing line and bow draw weight.
1 lb = 4.4482 N · 1 N = 0.2248 lb
Is Your “lbs” a Mass or a Force?
Strictly, a pound (lb) is a mass and a pound-force (lbf) is the force gravity puts on that mass. Everyday labels just say "lbs" for both. A bag of flour marked 5 lb means mass. A gas strut marked 100 lbs, a 20 lb fishing line or a 40 lb bow means force.
For converting to newtons, the difference almost never changes the answer. The pound-force is defined as the weight of 1 lb under standard gravity (9.80665 m/s²), so a 150 lb person weighs 667.2 N on Earth, and a force of 150 lbf is also 667.2 N. It only matters off Earth, or when a physics problem tells you to use a different value of g (see the homework section).
The Lbs to Newtons Formula
The factor 4.4482216152605 is exact: it is 0.45359237 kg (the international pound) times 9.80665 m/s². For mental arithmetic, × 4.5 gets you within about 1.2% (100 lb ≈ 450 N; exactly 444.8 N), and N ÷ 4.5 works the other way. For a rougher check, 1 N is about a quarter of a pound.
Worked Example: Replacing a 450 N Gas Strut
The gas strut holding up a car tailgate or toolbox lid is stamped "450N", but the replacements you can find are listed in pounds. Which one matches?
Step 1: Write down the formula
Step 2: Substitute the strut rating
Choose a 100 lb strut, which is 444.8 N, within 1.2% of the original. Strut forces come in steps, so pick the nearest one. Go too far below and the lid sags. Go too far above and it springs open and is hard to pull shut. Match the extended length and end fittings as well as the force.
Pound Ratings You Will Meet, in Newtons
Many products sold in the US give a force in pounds, while the metric version of the same product lists newtons. Some typical ratings:
| Rating | Pounds (lbf) | Newtons (N) |
|---|---|---|
| Maximum force to open an interior door (ADA) | 5 | 22.2 |
| 20 lb test fishing line (breaking strength) | 20 | 89 |
| 40 lb bow draw weight | 40 | 177.9 |
| 50 lb luggage scale limit | 50 | 222.4 |
| 100 lb gas strut | 100 | 444.8 |
| 300 lb pull-up bar rating | 300 | 1,334.5 |
The ADA Standards give the door figure as "5 pounds (22.2 N)", and the same 5 lbf limit applies to operating controls such as switches and handles. Fishing line "test" and pull-up bar ratings are the load at which the item is expected to fail or the maximum safe load, so they are forces even though they say "lb".
Physics Homework: Which g, and the kg Trap
Textbook problems often ask for the weight of something given in pounds. The SI route is weight = mass × g, so first convert pounds to kilograms (× 0.45359237). The most common mistake is skipping that step: 150 × 9.81 = 1,471.5 N is about 2.2 times too high, because 150 is a number of pounds, not kilograms.
The second source of disagreement is the value of g. This converter uses standard gravity, which is what defines the pound-force. If your course uses 9.8 or 9.81, your answer will differ slightly in the last digits:
| Gravity used | 150 lb in newtons |
|---|---|
| g = 9.8 m/s² | 666.8 |
| g = 9.81 m/s² | 667.5 |
| g = 9.80665 m/s² (standard, = lbf) | 667.2 |
All three are correct for their assumption. Use whichever g your teacher or textbook specifies, and give no more significant figures than the data supports.
Lbs to Newtons and Newtons to Lbs Tables
| lbf | N |
|---|---|
| 1 lb | 4.45 |
| 2 lb | 8.9 |
| 5 lb | 22.24 |
| 10 lb | 44.48 |
| 20 lb | 88.96 |
| 25 lb | 111.21 |
| 50 lb | 222.41 |
| 75 lb | 333.62 |
| 100 lb | 444.82 |
| 150 lb | 667.23 |
| 200 lb | 889.64 |
| 250 lb | 1,112.06 |
| 500 lb | 2,224.11 |
| 1,000 lb | 4,448.22 |
| N | lbf |
|---|---|
| 10 N | 2.25 |
| 50 N | 11.24 |
| 100 N | 22.48 |
| 150 N | 33.72 |
| 200 N | 44.96 |
| 250 N | 56.2 |
| 300 N | 67.44 |
| 400 N | 89.92 |
| 500 N | 112.4 |
| 600 N | 134.89 |
| 750 N | 168.61 |
| 1,000 N | 224.81 |
| 1,500 N | 337.21 |
| 2,000 N | 449.62 |
Tables are rounded to 2 decimal places. Need kips, tons-force, dynes or other units? The force converter shows a value in 14 force units at once.
Frequently asked questions
How many newtons is 1 lb?
1 lb (pound-force) is exactly 4.4482216152605 N, usually rounded to 4.448 N or 4.45 N. That is also the weight of a 1 lb mass on Earth under standard gravity.
How many pounds is 1 newton?
1 N is 0.2248 lbf, a little under a quarter of a pound. It takes about 4.45 newtons to make one pound.
Do I need to convert lbs to kg first?
Not with this converter, as the 4.448 factor already includes the conversion to kilograms. If you do the calculation as mass × g, then yes: convert pounds to kg first, or the answer comes out about 2.2 times too big.
Why does my textbook get a slightly different answer?
It probably uses g = 9.8 or 9.81 m/s² rather than standard gravity, 9.80665 m/s². For 150 lb that gives 666.8 N or 667.5 N instead of 667.2 N.
Is a newton bigger than a pound?
No. A pound-force is about 4.45 times bigger than a newton, so the number of newtons is always larger than the number of pounds for the same force.
Can I convert lbs to newtons on the Moon?
A force in lbf converts the same way anywhere. But a 1 lb mass on the Moon weighs only about 0.73 N, since lunar gravity is 1.62 m/s². The force converter has a weight-from-mass calculator for that.
Sources
- NIST Special Publication 811: pound-force to newton factor (4.448222) and the exact definition of the pound.
- 2010 ADA Standards for Accessible Design: sections 309.4 and 404.2.9, maximum operating and door-opening force of 5 pounds (22.2 N).
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