Spring unit converter
Convert length (in and mm), force (lbf and N), spring rate (lbf/in and N/mm) and torque (lbf·in and N·mm): the units springs are specified in.
Length
mm
=in
Force
N
=lbf
Spring rate
N/mm
=lbf/in
Torque
N·mm
=lbf·in
We standardize calculations in metric units (mm, N, MPa). Use this converter to work with imperial drawings and suppliers.
The key conversions: 1 in = 25.4 mm, 1 lbf = 4.448 N, 1 N/mm = 5.710 lbf/in and 1 N·mm = 0.00885 lbf·in.
Frequently asked questions
How do I convert a spring rate from N/mm to lbf/in?
Multiply by 5.710. A 4 N/mm spring equals 22.84 lbf/in. Going the other way, divide by 5.710.
Why do US catalogs use lbf/in?
Because the US industry specifies springs in inches and pounds-force. European and Brazilian drawings use N/mm. The calculators here show both systems side by side.
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