Enter the free length, the wire diameter, and the number of active coils into the Spring Pitch Calculator (unit options provided). The calculator will evaluate the spring pitch.

Spring Pitch Calculator

Enter any 3 values to calculate the missing variable

Related Calculators

Spring Pitch Formula

Spring pitch describes the average axial spacing assigned to each active coil in the model used by this calculator. It is useful when you know the overall spring length, the diameter term used in the equation, and the number of active coils, and you want a quick estimate of the pitch per coil.

SP = (L - 3*D)/NA

In this calculator:

Variable Meaning Typical Unit
SP Spring pitch length per coil
L Overall spring length entered into the calculator in, cm, m, ft
D Diameter value used in the formula 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:

L = NA*SP + 3*D
D = (L - NA*SP)/3
NA = (L - 3*D)/SP

How to Calculate Spring Pitch

  1. Measure or enter the spring length using one unit system only.
  2. Enter the diameter value in that same unit system.
  3. Count only the active coils, not coils that are inactive because of the end condition.
  4. Subtract three times the diameter term from the length.
  5. Divide that result by the number of active coils.

Using consistent units is essential. If length is entered in inches, diameter must also be in inches. If length is entered in centimeters, diameter must also be in centimeters.

Example

If the spring length is 5 in, the diameter is 0.25 in, and the number of active coils is 3, then:

SP = (5 - 3*0.25)/3
SP = 4.25/3
SP = 1.4167

The spring pitch is 1.4167 in/coil. That means each active coil is assigned about 1.42 inches of axial spacing on average within this formula model.

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 diameter term: 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.
  • If the entered length is too small relative to the diameter term, the computed pitch may become zero or negative, which indicates the inputs are not physically reasonable for this model.
  • 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.