Springs, components in many machinery, display numerous features, and 'solid height' is one of these features. It's useful to think about a spring in a car's suspension system when considering solid height, as its suitability can alter the comfort of the ride. This article will explore 'solid height', explain what it means, show how it influences design choices, and provide advice on selecting a spring with the correct solid height.

What is Solid Height?

The solid height of a spring refers to its minimum length under maximum compression. This is the point at which each coil is in direct contact with its neighbouring coils, leaving no room for further compression. This property becomes relevant in the context of design constraints or when calculating the load capacity of the spring.

Let's consider the design of a vehicle's suspension system as an example. Accurate calculation of a spring's solid height is a critical aspect of this task. Any error in this process can lead to the spring bottoming out or failing under high loads, which can impact the vehicle's performance and safety. Therefore, a clear comprehension of the spring's solid height is important for maintaining performance and safety standards.

However, the solid height is not the sole criterion for choosing a spring for a specific need. Other factors such as the spring rate, the type of material from which it's made, and its operating temperature also play significant roles in determining the spring's functionality. For example, a spring with a high solid height but a low spring rate may not be suitable for an application bearing heavy loads.A premature failure could occur even if the solid height appears sufficient. Therefore, while considering the solid height, engineers should also pay due attention to these other factors for achieving the most suitable spring configuration.

How Solid Height is Calculated

The solid height of a spring is determined by two factors: the wire diameter and the total number of coils. The diameter of the wire is the measurement of the wire's thickness, typically quantified using precise measuring tools such as calipers. The total number of coils is the count of complete revolutions that the wire makes in forming the spring. This can be counted visually.

The method to calculate the solid height involves straightforward multiplication of the diameter of the wire and the total number of coils. Let's suppose, for instance, a spring has a wire diameter of 2mm and consists of 10 coils. Here, the solid height is calculated by multiplying the two measurements, hence: 2mm * 10 = 20mm. It is important to keep the measuring units consistent. If the wire diameter has been measured in millimeters, the solid height will be calculated and reported in millimeters as well. Keep in mind that for certain end types such as grounded ends, this calculation changes due to some coils only counting partially towards the total height. For example, if a spring has ends ground such that half of a wire diameter is removed per end, the calculation becomes solid_height = wire_diam*(total_coils-1)

The wire diameter proportionately influences the carrying capacity of a spring. A spring with a larger wire diameter generally has a higher load capacity. To exemplify, consider a spring used in a safety valve. This type of spring, given the considerable pressure it is subjected to, would necessitate a wire of larger diameter. The resulting spring will thus have an increased solid height.

On the other hand, increasing the total number of coils to lower the solid height could affect the spring's rigidity and functioning. For instance, consider a clock spring, which requires a low solid height, implying more coils of thinner wire. This might result in reducing the torque output by the spring, consequently affecting the operation of the clock.

You can use a tool such as a compression spring calculator to obtain the solid height of a spring without manually calculating it.

What Happens if a Spring Compresses to its Solid Height?

When a spring is compressed to its solid height, where all the coils come into contact with one another, the characteristics of the spring change. Beyond the solid height, the spring cannot compress further, becoming a non-moving component within the mechanical system. In a practical scenario, consider a car's shock absorber - if the spring compresses to its solid height, it no longer has the capability to absorb additional impacts, leading to direct transfer of force to the car's structure. This could cause potential damage to both the car's structure and the spring due to excessive compression.

It is also possible that a compressed spring will not return to its initial form after releasing the compression force. This occurrence is referred to as 'set', which results in reduced spring effectiveness. For example, in a camera, the high-speed shutter operations frequently compress the springs to their solid height. This repeated compression can lead to 'set', causing the springs to lose their form and negatively impacting the camera's performance.

The solid height of a spring is an important parameter to consider when defining a spring's compression limits, with aims to avert malfunctioning and the deterioration of the spring's performance over time. Inclusion of the solid height parameter during spring selection, system design, and operation is a prerequisite for optimal outcomes.


Understanding a spring's solid height is crucial for correct spring selection and design. Errors when determining this measurement can lead to inaccurate use and misjudgments about a spring's abilities, which could result in damage to the equipment, failure of the spring, and safety issues. The solid height is not just a simple measurement, it's a key descriptor of a spring's potential. Correct calculation and use of the solid height in your designs contributes to achieving the best possible performance and long life of the springs and the systems they are used in.