Spring design hinges on identifying the correct number of coils in compression springs. This article introduces the calculation process for this number. We cover the distinction between total coils and active coils and discuss end types. We then touch on how the number of coils modulates the spring constant and, thereby, affects the behaviour of your springs. For example, springs with a lesser number of coils exhibit more stiffness and are prone to further distortion. This correlation between coils and spring performance reflects fundamental physics principles: fewer coils correlate with an increased force per coil, which raises the potential for deformation. Join us in this exploration to hone your spring designs.

Total Coils vs Active Coils

The terms 'total coils' and 'active coils' play a crucial role in the design and analysis of a compression spring. 'Total coils' refers to the entire series of coils in a compression spring, from one end to the other, including both active and inactive coils. Inactive coils are located at the ends of the spring and contribute to the alignment of the component without bearing load. On the other hand, 'active coils' are the load-bearing parts of the spring that compress when a load is applied to the spring. During the design process, it is critical to correctly calculate the number of active and inactive coils in the spring.

Both types of coils - active and inactive - influence the overall performance of the spring. For example, when dealing with high dynamic loads, the appropriate ratio of active to inactive coils can reduce the possibility of failures caused by buckling or coil clash. This is a result of the way the load is distributed within the spring.

The number of active coils in a compression spring can be calculated by subtracting the number of inactive coils from the total coil count. However, this calculation applies specifically to closed-end compression springs with inactive coils at both ends. For open-end compression springs, where all coils compress under load, all coils are deemed active. Hence, for open-end springs, the total number of coils equals the number of active coils.

How End Types Affect Number of Coils

The total number of coils in compression springs can be swayed by the type of ends used. The two most common types are closed and grounded and open ends. In springs with closed and grounded ends, the ends are ground in order to boost support and consistency. However, this design results in a reduction of active coils because the coils on the ends do not compress due to grounding.

Consider a spring that has 10 coils. If the spring has grounded ends, there would effectively be 8 active coils; two coils become inactive, one at each end. As a result, the choice of end type can directly alter the number of active coils, which can affect the spring's function and safety.

On the other hand, a spring with open ends will allow each coil to compress under applied force, thereby increasing the total number of active coils. When compared to the grounded end design, in an open-ended spring, more coils share the load. For a spring with grounded ends, a smaller number of active coils will bear the load. An open-ended design may lead to a higher load capacity, but the load distribution per coil will be different.

When deciding on the end type for your spring, it is necessary to take into account factors such as load capacity needs, safety requirements, and manufacturing constraints. These factors can affect the number of active coils in your compression spring design.

How Number of Coils Affects Spring Constant

The 'spring constant' quantifies a compression spring's stiffness by defining the force needed to compress the spring by a definable distance. The number of active coils in a spring plays a key role in determining this value. If a spring has more active coils, its spring constant, and thereby stiffness, decrease while its flexibility increases.

For example, designing a suspension system may require springs that can mitigate substantial shocks while preventing severe deformation. For this case, springs characterized by a high spring constant are needed. High spring constant implies fewer active coils.

Reducing the number of active coils increases the spring constant, resulting in a stiffer spring capable of withstanding heavier loads without much deformation. However, the material used to construct the spring and the diameter of the spring wire also influence the spring constant.

In compression spring design, the number of active coils should align with the required spring constant for the specific use. Adjustments in the number of active coils might be necessary to meet the stiffness requirements of a particular application. Also, remember to consider the impacts of wire diameter and material on the spring constant when performing calculations. Striking an optimal balance between these parameters ensures a design that fulfills the required spring characteristics.


Calculating the number of coils in a compression spring correctly is a skill needed in spring design and choice. This hinges on knowing the distinction between total and active coils, the effect of spring ends on the coil count, and the relationship between the spring constant and the coil number. Gaining this knowledge allows for the creation of spring designs that fit the specific requirements of your applications.