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Free Online Tool
Compression Spring Calculator — What It Works Out
This compression spring calculator turns a few dimensions into a full specification report: spring rate, safe load, maximum deflection, solid length, spring index and shear stress, with a live 3D preview. Enter the wire diameter, outside diameter and total coils, choose the material and end type, and press Calculate. It works in inches or millimetres.
Spring rate
Force per unit of deflection (N/mm or lbf/in) from the wire diameter, mean coil diameter, active coils and the material’s shear modulus.
Safe load and max deflection
The load at which the shear stress reaches the material’s allowable stress, and the deflection that load produces.
Solid length, index and pitch
Solid length, spring index, Wahl factor and pitch, plus warnings when the index is below 4 or above 12.
The formulas the calculator uses
Mean diameter D = OD − d Spring index C = D ÷ d Active coils Na = n − dead coils (open 0 · closed or closed & ground 2 · double-closed 3) Spring rate k = G · d⁴ ÷ (8 · D³ · Na) Wahl factor K = (4C − 1) ÷ (4C − 4) + 0.615 ÷ C Safe load F = τ(allow) · π · d³ ÷ (8 · K · D) Max deflection x = F ÷ k Solid length Ls ≈ n · d
d = wire diameter, OD = outside diameter, n = total coils, G = shear modulus of the wire. A step-by-step derivation is in our spring rate formula guide.
Worked example
Entering these values in the calculator above (metric, mild steel, closed ends) gives:
Input
Value
Wire diameter
2 mm
Outside diameter
20 mm
Total coils
12
End type
Closed ends
Material
Mild steel IS 4454 (G = 80,000 N/mm²)
Result
Value
Mean diameter / spring index
18 mm / 9
Active coils
10
Spring rate
2.743 N/mm
Wahl factor
1.1621
Solid length
24 mm
Safe load
63.1 N (6.43 kg)
Maximum deflection
22.99 mm
Shear stress at safe load
420 N/mm²
Check by hand: k = 80,000 × 2⁴ ÷ (8 × 18³ × 10) = 2.74 N/mm.
How to use the compression spring calculator
Choose units. Select English (inch) or Metric (mm). Compression is already selected as the spring type.
Enter the dimensions. Enter the wire diameter, outside diameter and total number of coils. Free length is optional; if left blank the calculator estimates it.
Select material and end type. Choose the wire material (music wire, hard drawn, stainless steel, mild steel and more), the end type and the direction of wind.
Calculate. Enter your name and 10-digit mobile number, then press Calculate.
Review and request a quote. Check the key results, the full specification sheet and the 3D preview, then send the specification to us on WhatsApp for a quote.
Frequently asked questions
How do I calculate the spring rate of a compression spring?
Spring rate k = G·d⁴ / (8·D³·Na), where G is the shear modulus of the wire, d the wire diameter, D the mean coil diameter (outside diameter minus wire diameter) and Na the number of active coils. Enter the dimensions above and the calculator does this for you.
What is the safe load shown in the results?
It is the load at which the shear stress in the wire reaches the allowable stress the calculator assumes for the chosen material. The allowable values are mid-range estimates, and real allowables also depend on wire size and duty, so treat the figure as a design guide.
How many active coils does a compression spring have?
Total coils minus the inactive end coils. The calculator uses 0 for open ends, 2 for closed or closed-and-ground ends and 3 for double-closed ends.
What spring index should I aim for?
Most springs are designed with an index (mean diameter ÷ wire diameter) between about 4 and 12. The calculator warns when the index is below 4 (hard to manufacture) or above 12 (tends to buckle or tangle).
Can I use inches as well as millimetres?
Yes. Switch between English (inch) and Metric (mm) at the top of the calculator; results follow the unit you choose.
How accurate are the results?
The calculation uses the standard design formulas. Manufacturing tolerance on wire and coil diameter normally makes a real spring’s rate vary by roughly ±10% from the theoretical value.
Can you manufacture the spring I design here?
Yes. Send the specification to Gurudatta Trading Co. on WhatsApp from the results page and we will quote and make it to your drawing or sample.