Spring Unit Converter
Convert the units engineers use to design and specify springs — rate, stress, torque, force and more — and see the exact factor behind every result. Free to use, metric and imperial, no sign-in.
Length
Linear dimensions and deflection
About Length conversions
Length units measure linear dimensions in a spring design — wire diameter, coil diameter, free length, solid height and deflection.
Wire and coil diameters are usually given in inches (US) or millimetres (metric).
Quick reference — Length
Figure out the specs you need
Got your numbers but not sure what spring they add up to? Share your loads, rates, and dimensions and a Lee Spring engineer will help you dial in the right stock or custom spring.
FAQs
How do I convert spring rate from lbf/in to N/mm?
To convert spring rate from lbf/in to N/mm, multiply by 0.17513. For example, 10 lbf/in equals 1.7513 N/mm. In the converter, choose the Spring Rate category, set the "from" units to lbf and in, set the "to" units to N and mm, then type your value.
What is the conversion factor from lbf to N?
One pound-force (lbf) equals 4.4482 newtons (N), and one newton equals 0.2248 lbf. Use the Force category to convert spring loads between the two unit systems.
What units are used for spring stress?
Spring stress is given in psi or ksi in the United States and in MPa or N/mm² in most other countries. 1 MPa equals 1 N/mm² exactly, and 1 ksi equals 6.895 MPa. The Stress category converts between all of these.
What is the difference between lbf and lb?
lbf (pound-force) measures force, such as the load a spring pushes or pulls with. lb (pound) measures mass, such as the weight of wire or a finished part. Spring loads are always specified in lbf, so this tool keeps Force and Mass in separate categories.
How do I convert torque from in-lbf to N-m?
One inch-pound of torque (in-lbf) equals 0.113 newton-meters (N-m), and one foot-pound equals 1.356 N-m. Choose the Torque category, then set the force and length units on each side to convert.
How do I convert torsion spring rate?
Torsion spring rate is torque per unit of angle, for example in-lbf/deg or N-mm/deg. Pick the Torsion Rate category, set the force, length, and angle units on both sides, then enter your value. Always check whether the rate is quoted per degree, per radian, or per turn, because each gives a very different number.
Can I convert a whole list of values at once?
Yes. Switch to Batch mode and paste your numbers, one per line or separated by commas. Every value is converted using the units you selected, and you can copy the results table or export it as a CSV file.
Can I share or print a conversion?
Yes. The "Copy link" button gives you a URL that reopens the exact conversion you are viewing, which is handy for emails and RFQs. The "Print" button produces a clean copy of the result for your records.
Can I convert temperatures for heat treatment?
Yes. The Temperature category converts between Fahrenheit, Celsius, and Kelvin, which helps when you are reading heat-treatment, stress-relief, or operating-temperature limits for spring materials.