If you're an engineer, relevant knowledge about spring rates is essential for designing and selecting springs. This concept is critical to a spring's function when placed under a load and is used in a wide array of applications  including bicycle suspensions. This guide will help you understand compression spring rates further, by breaking it down into simple, comprehensible segments. It will cover not just the fundamental knowledge but will also highlight the often missed subtleties. This comprehensive guide on compression spring rates provides clear and detailed information, including specific exceptions that come into play.
What is Spring Rate?
Spring rate denotes the force required to compress a spring by a certain unit length. Expressing this attribute in terms of force per unit length, with units like Newtons per millimeter (N/mm) or pounds per inch (lb/in), provides clarity on the spring's behavior under external force. For compression springs, the spring rate communicates the necessary compression force. A spring with a higher spring rate requires more force for compression, whereas a spring with a lower spring rate requires less force.
Selecting a spring for an application often involves an evaluation of stiffness or flexibility. For example, in a mechanical design that necessitates gentle and buffered movements, a spring with a lower spring rate may be appropriate. Conversely, designs that need to endure substantial forces may benefit from a spring with a higher spring rate.
Moreover, spring rate selection should be in direct correlation with design and operational specifications of a particular application. For supporting a high load, a spring with a higher spring rate is suitable. Conversely, when designing an application for damping vibrations, a spring with a lower spring rate may be the better choice. These specific examples demonstrate how comprehension of spring rates can aid in selecting the optimal spring for a specific application.
How to Calculate Spring Rate of a Compression Spring
The spring rate (k) for a compression spring is determined as the ratio between the change in force (ΔF) and the change in length (ΔL). In mathematical terms, this relationship can be represented with the formula: k = ΔF / ΔL.
Observe the following steps to utilize this formula:

Measure initial length: Measure and record the starting length of the compression spring (L1) in the absence of applied force.

Apply force and measure: Subsequently, exert a measurable force (F1) on the spring and measure the resulting length of the spring (L2).

Calculate changes: Calculate the change in length (ΔL) using the formula L2 – L1 and the change in force (ΔF) with the formula F2 – F1.

Compute spring rate: Now use the spring rate formula, k = ΔF / ΔL, to compute the spring rate.
This calculation assumes that the compression spring complies with Hooke's Law. According to this law, the deformation of a spring, caused by the application of force, is directly in proportion to the force itself. However, this ratio may deviate from a linear nature when the spring is exposed to substantial forces. During such scenarios, the spring's response may be observed to be nonlinear in nature. For such instances, accumulate multiple force and length measurements to calculate an average spring rate. For instance, apply three different amounts of force to the spring and measure the corresponding change in length for each. Utilize these measurements to calculate individual spring rates and compute an average to obtain a more accurate spring rate for springs that exhibit nonlinear deformation.
Conclusion
Calculate the compression spring rate correctly for optimal use of a spring in your engineering projects. This calculation positively impacts the relationship between force and displacement and assists in selecting appropriate springs. Accurate spring rate calculation is central in designing and using compression springs. The spring rate has practical uses, playing a significant role in the success of your projects.