ETAR ENGINEERING TOOL
Spring calculator
Explore compression, extension and torsion springs with a transparent, first-pass model. Adjust the geometry, compare alternatives and take the assumptions with you.
01 / INPUT
Your starting point
What do these symbols mean?
- d
- Wire diameter
- D
- Mean coil diameter
- C
- Spring index D/d
- n
- Active turns
- F₀
- Initial tension (extension)
- r
- Perpendicular force arm (torsion)
02 / RESULTS
Your calculation
A first look at your design
Enter a few dimensions and calculate to see the rate, load and a force–travel chart.
Mean diameter — mmSpring index —Active turns —
Loaded length — mmApprox. solid length — mmTravel to solid — mm
Opening work — JInitial tension — N
Torque — N·mmWork — J
Force vs travel
Theoretical body response · linear model
| s (mm) | F (N) |
|---|---|
| — | — |
| — | — |
| — | — |
Take this estimate to your project
Copy the summary into your inquiry. Add the application, working loads, installation, environment, expected cycles and quantity. You can attach a drawing or the printed PDF in the contact form.
Discuss manufacturing with ETARCompare alternatives
0 / 3Save a calculated version to compare its assumptions and results.
| Version | Wire d mm | Mean D mm | n | k N/mm | F N | Stress MPa | Action |
|---|
Preliminary analytical estimate. Results describe an idealized spring body; they do not confirm a manufactured design, material strength, fatigue life or safety factor.
ETAR · PRELIMINARY DESIGN RECORD
Spring calculation
No current calculation. Recalculate before printing a design record.
Entered design and result
Model assumptions
Warnings
Preliminary idealized body model. This record is not a validated design or a material approval.
HOW TO USE THIS TOOL
A useful estimate with its assumptions in view
Choose a spring
The first version models cylindrical helical springs made from round wire: compression, extension and torsion.
Enter known dimensions
Use millimetres and newtons. The decimal comma or point are both accepted; thousands separators are not.
Compare, then review
Check the notes and ask ETAR engineering to assess the complete geometry, material, process and intended duty.
METHOD & SCOPE
Simple, inspectable engineering relationships
The model uses shear modulus G for compression and extension, and Young's modulus E for bending in torsion. A corrected Wahl factor estimates body stress in compression/extension; torsion uses an inside-fibre curvature correction.
Core equations
Compression / extension: k = G·d⁴ / (8·D³·n); F = k·s (compression) or F = F₀ + k·s (extension). Body shear stress: τ = KW·8·F·D / (π·d³). Torsion: kθ = E·d⁴ / (10.8·D·n·360) N·mm/°; its empirical 10.8 factor represents average internal friction. Inner-fibre bending stress: σ ≈ K_i·32·M / (π·d³). These apply to the idealized round-wire coil body only.
K_W = (4C−1)/(4C−4) + 0.615/C (Wahl); K_i = (4C²−C−1)/(4C(C−1)); C = D/d. G is shear modulus; E is Young modulus.