How to use this calculator
- Choose the solve mode. Use pitch from free length for an existing spring, or free length from pitch for a layout target.
- Enter wire and active coils. Wire diameter and active-coil count define the active body spacing calculation.
- Select the end type. Closed-ground, closed/squared and open/plain ends use different simplified solid-height stacks.
- Enter the working deflection. The working deflection is compared with travel to solid so coil-bind clearance stays visible.
- Read pitch and clearance. Use body pitch, active-coil gap, travel to solid and working clearance before moving into rate or stress checks.
How it works
This worksheet isolates the compression-spring geometry behind solid height, open body pitch and coil-bind clearance. Solid height is the wire stack at full compression. The end type controls the simplified inactive-coil allowance: closed & ground: Ls = d x (Na + 2) closed / squared: Ls = d x (Na + 3) open / plain: Ls = d x (Na + 1)
When free length is known, the open body pitch estimate spreads the
available travel evenly across the active coils:
p = d + (L0 - Ls) / Na
The active-coil gap is p - d. If you instead know the
desired body pitch, the calculator reverses the same relation:
L0 = Ls + Na x (p - d)
Use this before rate and stress checks. Once the geometry has reasonable travel to solid, carry the same wire, coil and free-length values to the compression spring calculator for spring rate, Wahl-corrected stress and buckling. For a known load, use spring deflection under load or spring force.
Worked example
Verified against the live calculator
With d = 1.0 mm, Na = 8, closed & ground
ends and L0 = 40 mm, the modeled solid height is
1 x (8 + 2) = 10 mm. Travel to solid is
40 - 10 = 30 mm. Body pitch is
1 + 30 / 8 = 4.75 mm, so the active-coil gap is
3.75 mm. At 10 mm working deflection, the
spring length is 30 mm and clearance to solid is
20 mm.
Spring material data
This page uses geometry only; it does not need material constants. Rate, stress, fatigue and set calculations depend on material data and belong in the spring rate or compression spring workflows.
| Check | Formula | Use |
|---|---|---|
| Closed & ground solid height | Ls = d x (Na + 2) | Common squared-and-ground compression spring seating model. |
| Closed / squared solid height | Ls = d x (Na + 3) | Adds a taller stack allowance for unground closed ends. |
| Open / plain solid height | Ls = d x (Na + 1) | Plain-end first-pass stack model. |
| Travel to solid | L0 - Ls | Maximum compression travel before coil bind, before safety margin. |
| Body pitch | p = d + (L0 - Ls) / Na | Approximate open active-coil center-to-center pitch. |
| Free length from pitch | L0 = Ls + Na x (p - d) | Reverse layout when a target active-body pitch is known. |
| Working clearance | L0 - x - Ls | Remaining clearance to solid at the entered deflection. |
Source: Standard helical compression-spring layout formulas; verify final end geometry, grinding allowance, preset and tolerances against the spring drawing or supplier data.
Pitch and solid height set the finite travel limit. For a dedicated stability check, carry the same free length and end type into the spring buckling calculator.
Frequently asked questions
What is spring pitch?
Spring pitch is the center-to-center axial distance between adjacent active coils in the open body of the spring. In this calculator, p = d + (L0 - Ls) / Na.
How do I calculate compression spring solid height?
Multiply wire diameter by the modeled coil stack. Closed & ground ends use Ls = d x (Na + 2), closed/squared ends use Ls = d x (Na + 3), and open/plain ends use Ls = d x (Na + 1).
Can this solve free length from a target pitch?
Yes. Switch the solve mode to free length from pitch. The calculator uses L0 = Ls + Na x (p - d), then reports travel to solid and working clearance.
Is active-coil gap the same as pitch?
No. Pitch is center-to-center. Active-coil gap is the open axial space between wire turns, so gap = p - d.
Does this calculate spring rate or stress?
No. This page is for geometry only. Use the compression spring calculator for spring rate, Wahl-corrected stress, buckling and force at deflection.
Method & assumptions
- Compression-spring body geometry only; extension-spring hooks and torsion-spring legs are different workflows.
- Pitch is the active body pitch at free length, not a detailed drawing of closed-end transition turns.
- Solid-height models are simplified screening stacks; supplier drawings can add grinding allowance, preset, set allowance and tolerance.
- Working clearance to solid is not a recommended safety margin. Choose production clearance from the application, tolerances, surge and fatigue requirements.
- Rate, stress, buckling, fatigue, relaxation and permanent set are not calculated here.