newton per mm to lbs per inch
N/mm and lbs/in are the two dialects of spring rate — how much force a spring adds per unit of compression. Coilover shoppers meet both constantly; this converter translates exactly between them.
The Converter
N/mm → lbf/inTotal Working
| Newtons per millimeter (N/mm) | Pounds per inch (lbf/in) |
|---|---|
| 1 | 5.7101 |
| 5 | 28.5507 |
| 10 | 57.1015 |
| 20 | 114.2029 |
| 30 | 171.3044 |
| 40 | 228.4059 |
| 50 | 285.5074 |
| 60 | 342.6088 |
| 80 | 456.8118 |
| 100 | 571.0147 |
The exact factor
1 N/mm = 5.7101471547 lbf/in
Derived from the defined constants 1 lb = 0.45359237 kg and gₙ = 9.80665 m/s² — no measurement error, only display rounding.
Master converter
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Newtons To LBS home →How the spring-rate factor works
Convert the force and the length separately: 1 N = 0.2248089431 lbf, and one millimeter of travel is 1/25.4 of an inch — so per inch you get 25.4× the force. Multiply: 0.2248089 × 25.4 = 5.7101472.
Example: an 8 kg/mm-equivalent coilover spring of 78.5 N/mm converts to 78.5 × 5.71015 = 448.2 lbf/in — sold in the US as a “450 lb spring”.
Reading spring catalogs
Japanese and European catalogs list N/mm (or kgf/mm — multiply kgf/mm by 9.80665 to get N/mm first). US catalogs list lbs/in. Typical passenger-car rates run 20–60 N/mm (115–345 lbf/in); motorsport springs run far higher.
Mixing the units up by 5.7× is a common and expensive suspension-ordering mistake — always convert, never assume.
Frequently asked
What is 10 N/mm in lbs per inch? +
How do I convert kg/mm spring rates? +
How do I go from lbs/in back to N/mm? +
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