Spring Wire Size Calculator
SI
Imp
Imperial
Inputs
View results
Target spring rate
(k)
Required stiffness of the spring.
N/mm
Mean coil diameter
(D)
Center-to-center coil diameter. Outside diameter will be D + wire diameter.
mm
Active coils
(Nₐ)
Coils that actually deflect under load.
Free length
(L₀)
Unloaded length used for solid height and travel checks.
mm
Working deflection
(x)
Deflection used to calculate force and stress after the wire size is solved.
mm
Material
Sets shear modulus and allowable stress.
Music wire (ASTM A228)
Oil-tempered (ASTM A229)
Hard-drawn (ASTM A227)
Chrome silicon (ASTM A401)
Chrome vanadium (ASTM A232)
Stainless 302/304 (ASTM A313)
End type
Sets inactive end coils and solid height.
Closed & ground
Closed (squared)
Open (plain)
Results
Default result
Edit inputs
Required wire diameter
(d)
1
mm
Pass
Also computed
Outside diameter
(OD)
11
mm
Inside diameter
(ID)
Pass
9
mm
Spring index
(C)
Pass
10
Force at deflection
(F)
12.39
N
Corrected shear stress
(τ)
Pass
361.2
MPa
Allowable shear stress
995
MPa
Solid height
10
mm
Travel to solid
30
mm
Show 2 more results
Method notes
3 notes
Wire diameter is solved from d = (8·k·D³·Nₐ / G)^(1/4).
Because rate depends on d⁴, small wire-diameter changes strongly affect spring rate.
Check stress, spring index and travel-to-solid before treating the wire size as usable.
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