Skip to content

What to Know About Spring Compression Formulas and Measurement

There’s a lot you need to know about spring compression formulas and measurement because they can help you to design a quality spring that stands the test of time.

Spring Compression Formulas and Measurement - KB Delta

The proper use of these metrics also determines how the quality of one spring differs from another.

Generally, a good use of formulas and measurement can enable you to calculate compression spring design from the knowledge of the parameters that are used to form the spring.

The formulas were elaborated and globally accepted as the standards that will be used to determine a spring’s design.


What is Compression Spring Measurement?

Compression spring measurement is a process that enables you to determine the accurate and precise parameters that are important to your spring’s design.

Some of these parameters are the length of the wire, the working loads, and the compression spring’s constant k.

The tools that are employed to carry out these measurements include a ruler, dial calipers, and a micrometer.

It can, therefore, be said that there are various spring designs and knowing the right measurement for a particular type you’re out to get will help you to ascertain the best spring that will meet your needs.


Elements to Determine While Calculating a Compression Spring

The process of measuring a compressor spring requires that you know the following diameter parameters and these are:

  • Total Coils
  • Free Length
  • Wire Diameter
  • Inner Diameter
  • Outer Diameter

Let’s take a look at each element:

1. Total Coils:

The total coils count is a measure of each complete rotation and what’s left of the last coil.

2. Free Length:

The free length of an uncompressed spring can be easily determined using dial calipers and placing them on the full length of the spring.

Wondering what is a dial caliper?

A dial caliper is a tool that enables you to get a more exact measurement of a spring.

This measurement is usually required to be accurate since it could potentially affect the rate and travel of the spring.

3. Wire Diameter:

Placement of the calipers on the wire from the center of the spring can help to determine the wire’s diameter.

4. Outer Diameter:

The outer diameter is determined by aligning the dial calipers on the outer part of the coil’s width.

5. Inner Diameter:

The inner diameter of spring is the width of the interior part of the coil’s diameter to the helix.

The formula that is relied upon to ascertain this is inner diameter is I.D. = O.D. – 2d.

The 2d, in this case, stands for the two wire diameters.

It’s also worthy to note that it may sometimes be difficult to get the accurate measurement of the inner diameter.


What are Compression Spring Ends?

Compression spring ends are other elements that need to be ascertained to get a good measurement of your spring.

The different types of spring ends are:

  • Open Ends
  • Closed and Square
  • Closed and Ground
  • Double Closed and Square Ends

1. Open Ends:

Spring ends are said to be open because the ends remain open and do not have a pitch.

As a result, a spring with open ends has all its coils active.

2. Closed and Square:

These are the opposite of open-ended springs since the ends are closed but still do not have a pitch.

What this means is that unlike open ends, only some of the coils in the spring will be active and these are those that feature a pitch.

Similarly, the active ones can be determined by subtracting two from the total coils.

Active coils = Total Coils – 2

3. Closed and Ground:

Closed and ground are quite similar to closed and square ends but there’s still a unique difference.

Here, the ends undergo a grinding process where the first and last coils have half a wire diameter ground from them.

This allows the spring to stand upright in a vertical position.

Like closed and square ends, you can also determine active coils with the formula:

Active Coils = Total Coils – 2

4. Double Closed and Square ends:

The ends of these coils are closed, however, the first two and last two coils come in contact.

The active coils can be determined just by subtracting 4 from the total number of coils.

It is given by:

Active Coils: Total Coils – 4


Our Types of Compression Springs - KB Delta


Spring Compression Formulas

Now that you know the metrics, we’ve also outlined the formulas that are used to determine a compression spring’s design.

These formulas have been adopted in creating spring calculator that will save the time and effort of doing it manually.

They are:

  • Solid Height Formulas
  • Spring Diameter Formulas
  • Wire Length Formulas
  • Spring Index Formula
  • Load and Travel Formulas

1. Solid Height Formulas:

Solid height (Lsolid) can be calculated by adding an extra wire to the total coils (N) before the result is multiplied with the wire diameter (d).

If the spring has ground ends, you will only have to find the product of the wire thickness and the total coils.

This is because grinding the end leads to the last coil being equivalent to half the diameter.

A more mathematical approach to finding solid height is:

  • Solid Height (Lsolid) = Wire Diameter (d) x (Total Coils + 1)

For cases where there are ground ends, you’ll have:

  • Solid Height = Wire Diameter x Total Coils

Which is equivalent to L solid = dN

2. Spring Diameter Formulas:

In order to calculate the compression spring’s diameters, you need to determine the diameter elements and differentiate one from the other.

The elements, in this case, are the inner diameter (D inner), wire diameter (d), and outer diameter (D outer).

What’s required to find the inner diameter is to multiply the wire diameter by two before subtracting the result you’ve obtained with the outer diameter.

On the contrary, the outer diameter can be obtained by multiplying the wire’s diameter by two and then adding the result to the inner diameter which is the opposite of the latter.

There’s also the mean diameter (D) to consider and its value ranges between the inner and outer diameter since it is the coil’s diameter which runs from the center of the wire.

Thus, there may be a need to find the difference between one wire diameter and the outer diameter or add the inner diameter with one wire diameter.

The formula that can be employed in each case is:

  • Inner Diameter = Outer Diameter – 2 (Wire Diameter)
    Expressed as D inner = D outer – 2d
  • Outer Diameter = Inner Diameter + 2 (Wire Diameter)
    Expressed as D outer = D inner + 2d
  • Mean Diameter = Outer Diameter – Wire Diameter
    D = D outer – d


  • Mean Diameter = Inner Diameter + Wire Diameter
    D = D inner + d

This is an incredibly important part of determining the proper measurements.

3. Wire Length Formulas:

There’s also the ability to be able to calculate the length of the compression spring which can give you a good idea of the actual material that is best for the manufacture of these springs.

Knowledge of the wire length of one coil (cL) begins by multiplying the wire’s mean diameter with pi (3.14 or π).

The next step is to find the total compression spring wire length (tL) by multiplying the wire length of one coil (cL) with the total amount of coils (N).

The above is mathematically represented as:

  • Coil Wire Length = Mean Diameter x Pi
    cL = Dπ
  • Total Wire Length = Coil Wire Length x Total Coils
    tL = cL x N

4. Spring Index Formula:

The spring index enables you to accurately determine the tightness of your coil and manufacturing difficulty of the compression spring.

Consequently, this calculation of the spring index requires a division of the mean diameter (D) by the wire diameter (d).

  • Spring Index = Mean Diameter ÷ Wire Diameter
    I = D ÷ d

5. Load and Travel Formulas:

You can calculate the working loads of your coil with the use of load and travel compression spring formulas.

The aim is to ascertain if the spring to be manufactured will be able to handle the load and travel the distance expected.

Calculating the working load involves multiplying the distance covered by the spring rate.

On the other hand, you can calculate the distance traveled by dividing the load by the spring rate.

Here’s what it looks like:

  • Load = Travel x Rate
    L = Tk
  • Travel = Load ÷ Rate
    T = L ÷ k



After going through the above, you’ll agree that what to know about spring compression formulas and measurement are numerous.

If you’re a perfectionist that wants the weight, length, rate, travel, and other elements of your spring to be perfect, then it starts with employing these formulas and measurements where they apply.

Remember, every inch counts and could make or mar the quality of compression springs you’re trying to create and if your aim is to maintain your reputation as a manufacturer, it begins with holding each of these formulas in high esteem.


Contact Us for Springs - KB Delta

Posted in
Skip to content