Mechanical

Spring Calculator

Calculate compression and extension spring force, rate, and dimensions.

Input Parameters

Units:
in
in
in

Results

Enter spring dimensions and click Calculate

What is a Compression Spring Calculator?

A compression spring calculator determines the spring rate, load capacity, and stress levels for helical compression springs based on their physical dimensions and material properties.

These calculations are essential for selecting or designing springs that meet force requirements while staying within safe stress limits for reliable operation and fatigue life.

How to Use

  1. Enter the wire diameter (measure with micrometer for accuracy)
  2. Enter the outer diameter of the spring
  3. Enter the free length (unloaded spring height)
  4. Count and enter total coils (including inactive end coils)
  5. Select the end type and material
  6. Click Calculate to see spring characteristics

FAQs

Spring rate (k) is the force required to deflect a spring by one unit of length. For compression springs: k = (G × d⁴) / (8 × D³ × Na), where G is shear modulus, d is wire diameter, D is mean coil diameter, and Na is active coils. Higher wire diameter or fewer coils increase rate.

Spring index (C) is the ratio of mean coil diameter to wire diameter (D/d). An index of 4-12 is ideal. Below 4, the spring is too tight to manufacture economically and has high internal stresses. Above 12, the spring may be prone to tangling and buckling.

Closed & Ground ends are most common - they provide flat bearing surfaces and predictable solid height. Closed (not ground) is less expensive but may not sit square. Open ends are used for extension springs or where squareness isn't critical. Open & Ground provides one flat end.

Springs buckle when free length/mean diameter exceeds about 4:1 for fixed-free ends or 5.2:1 for fixed-guided ends. Solutions include using a larger diameter wire, increasing coil diameter, reducing free length, or guiding the spring in a tube or over a rod.

Music wire (ASTM A228) offers the highest strength and is most common. Chrome vanadium and chrome silicon handle higher temperatures and shock loads. Stainless steel for corrosion resistance. Phosphor bronze and beryllium copper for electrical conductivity and non-magnetic applications.

Limitations

  • • Calculations assume ideal helical compression springs
  • • Does not account for buckling - check length/diameter ratio separately
  • • Fatigue life depends on stress ratio and surface finish
  • • High temperature reduces material strength - derate accordingly
  • • Verify critical applications with physical testing

Further Reading

Spring Rate Calculator: How to Calculate Spring Constant

Learn spring rate formulas for compression and extension springs. Covers wire diameter, coil count, and material selection.

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