Calculate spring pitch from free length, wire diameter and active coils for a closed-end compression spring, or solve for any one of the other values.
Related Calculators
- Frequency Displacement Acceleration Calculator
- Modulus Of Toughness Calculator
- Toggle Force Calculator
- Hydraulic Force Calculator
- All Physics Calculators
Spring Pitch Formula
Spring pitch is the axial distance from one wire centerline to the next. This calculator assumes a uniform-pitch compression spring with closed, unground ends and about two inactive end coils: L = 3d + NA × SP. Other end finishes require different allowances.
In this calculator:
| Variable | Meaning | Typical Unit |
|---|---|---|
| SP | Spring pitch | length (wire-center spacing) |
| L | Free spring length | in, cm, m, ft |
| D | Wire diameter, not coil diameter | same unit as length |
| NA | Number of active coils | coils |
The result is an average pitch, which means it represents spacing per active coil based on the entered geometry. It is most helpful for quick checks, comparison of spring layouts, and verifying whether a spring becomes more tightly or more loosely wound as one design variable changes.
Rearranged Equations
Because the calculator can solve for a missing value, the same relationship can be rearranged as follows:
How to Calculate Spring Pitch
- Measure the free spring length and select its unit.
- Enter the wire diameter and select its unit.
- Count only the active coils, not coils that are inactive because of the end condition.
- Subtract three times the diameter term from the length.
- Divide that result by the number of active coils.
The calculator converts selected length units before applying the formula. For manual calculations, use the same units for free length, wire diameter and pitch.
Example
If the spring length is 5 in, the diameter is 0.25 in, and the number of active coils is 3, then:
The spring pitch is 1.4167 in, measured wire-center to wire-center. The clear gap is approximately 1.1667 in after subtracting the 0.25-in wire diameter.
How to Interpret the Result
- Larger pitch: coils are spaced farther apart on average.
- Smaller pitch: coils are packed more closely together.
- More active coils: pitch decreases if length and diameter stay the same.
- Longer spring length: pitch increases if diameter and active coils stay the same.
- Larger wire diameter: pitch decreases if length and active coils stay the same.
Practical Notes
- This equation gives an average pitch, so it is best suited to springs with fairly uniform spacing.
- If the spring has variable pitch, progressive winding, or unusual end geometry, the average result may not match the spacing at every coil location.
- The number of active coils must be greater than zero.
- Pitch must exceed wire diameter for positive clearance between active coils. A zero or negative result, or overlapping turns, is rejected. Geometry alone does not establish safe travel or spring strength.
- For the cleanest result, use measured values with consistent precision, especially when dealing with small wire diameters or springs with many coils.
Common Questions
- What is an active coil?
- An active coil is a coil that contributes to spring deflection during loading. End coils that are fixed, ground, or otherwise inactive should generally not be counted as active coils.
- Why does unit consistency matter?
- The formula combines length and diameter directly. If those values use different units, the result will be incorrect even if the arithmetic is done properly.
- Can this calculator be used for quick spring comparisons?
- Yes. It is helpful when comparing candidate spring geometries, checking whether spacing trends make sense, or solving for a missing variable when three values are already known.
- Is the result the exact spacing between every coil?
- No. It is an average value derived from the equation shown above. Springs with nonuniform winding may have local coil spacing that differs from the calculated result.
