How to Measure Gas Struts Guide

Understanding Gas Strut Basics and Why Measurement Matters

Gas struts, also called gas springs or pneumatic struts, are mechanical devices filled with pressurized nitrogen gas that help lift, lower, or hold objects in place. They work by using compressed gas to create a pushing or pulling force, making them useful for automotive hoods, truck beds, cabinet doors, and industrial equipment. Unlike traditional springs made of metal coils, gas struts contain sealed chambers with pressurized gas that provides consistent force throughout their range of motion.

Understanding how gas struts function helps explain why accurate measurement is critical. The gas inside creates pressure measured in pounds per square inch (PSI). When you compress a gas strut, the gas inside compresses further, resisting the motion. When you release it, the pressurized gas pushes back, helping to lift or support weight. The effectiveness of any gas strut depends on several factors: the amount of gas pressure inside, the surface area of the internal piston, and the length of the strut itself.

Measuring gas struts correctly matters because using the wrong size or pressure rating can cause several problems. An underpowered strut may not lift the object fully or may fail prematurely. An overpowered strut can slam objects shut too quickly or create safety hazards. In automotive applications, incorrect strut measurements can affect hood operation, trunk performance, and even vehicle safety. For industrial and furniture applications, wrong measurements can lead to equipment damage or worker injury.

Gas struts come in standardized sizes, but there is significant variation in pressure ratings and lengths. A typical automotive hood strut might range from 100 to 200 pounds of force, while industrial struts can exceed 500 pounds. Measuring your existing struts or determining the right specifications for new installation requires understanding the basic dimensions and force requirements of your specific application.

Practical Takeaway: Before measuring gas struts, identify what application you're working with—automotive, furniture, industrial equipment, or something else—because this determines what measurements matter most and what pressure ranges are typical for your situation.

Measuring Strut Length and Mounting Distance

The most fundamental measurement for any gas strut is its length. Gas struts have two different length measurements: the compressed length (also called closed length) and the extended length (also called open length). These measurements determine whether a strut will physically fit in your installation space and how much clearance you need when the strut is fully extended or compressed.

To measure compressed length, push the gas strut inward as far as it will go by hand or with a tool, then measure from the center of the top mount point to the center of the bottom mount point. This measurement tells you the minimum space the strut occupies. Compressed length for most automotive struts ranges from 8 to 14 inches, while industrial struts can be longer. Write this number down clearly—this is critical information when ordering replacement struts.

Extended length is measured when the strut is fully extended and pushed outward as far as it will go. Measure from the center of the top mount point to the center of the bottom mount point in this fully extended position. This measurement determines the maximum reach of the strut and tells you how much space it will take up when fully deployed. Extended length is always larger than compressed length—often by 4 to 8 inches depending on the strut design. The difference between these two numbers is called the stroke length, which represents how much the strut can move.

Beyond these basic measurements, you need to identify the mounting distance, which is the space between where the top and bottom of the strut attach to your equipment or vehicle. This measurement must fall within the strut's range. For example, if your mounting points are 12 inches apart when the equipment is closed, and 18 inches apart when fully open, you need a strut with a compressed length of approximately 12 inches and an extended length of approximately 18 inches. Struts with too-short extended lengths won't open the equipment fully. Struts with too-long compressed lengths won't fit when the equipment is closed.

When measuring mounting distance, account for any mounting brackets or hardware that might affect the actual measurement point. Measure from the center of one mount hole to the center of the opposite mount hole, not from the outer edges. If your equipment has existing struts, measure from their mount points. If you're installing new struts in an existing space, measure the actual distance between where you'll install the top and bottom attachment points.

Practical Takeaway: Always record three numbers: compressed length, extended length, and mounting distance (both when closed and when fully open). These three measurements together tell you whether a strut will physically work in your application.

Determining Pressure and Force Requirements

Gas strut pressure, measured in PSI (pounds per square inch), directly relates to the force the strut produces, typically measured in pounds or Newtons. Understanding the difference between these two measurements and how they connect to your application is essential for selecting the correct replacement strut. The force a gas strut produces depends on both its internal pressure and the size of its internal piston—a larger piston area with the same pressure produces more force.

To determine what pressure or force you need, first identify what weight or load the strut must support or lift. For automotive applications like hoods or trunks, this is typically the weight of the hood or trunk lid itself, often ranging from 30 to 100 pounds depending on the vehicle. For furniture applications like cabinet doors or desk lids, this might be 10 to 50 pounds. For industrial equipment, loads can range from 100 to 1,000 pounds or more. Weigh the object if possible by placing it on a bathroom scale or having it weighed at a hardware store.

If you have an existing gas strut that's working correctly, you can look for its specifications marked on the strut itself. Most quality gas struts have markings that include the pressure rating, usually expressed as something like "100N" (Newtons) or "25 lbs" (pounds of force). Newtons and pounds both measure force—one pound equals approximately 4.45 Newtons. If a strut is marked "100N," that's roughly equivalent to 22.5 pounds of force. These markings may be printed on the strut body, on a label, or on a metal tag attached to the strut.

The rule for gas strut force selection is that the strut's total force should typically equal about 50 to 75 percent of the load weight if you're supporting the load. This accounts for friction in hinges and mounting brackets. For example, if you're supporting a 60-pound hood, you'd want a strut rated for approximately 30 to 45 pounds of force (50 to 75 percent of 60). If you're lifting a 60-pound door open with the strut, you might use a slightly higher force rating to ensure it opens easily. However, if the strut force exceeds 100 percent of the load, the equipment may open too quickly or be difficult to close, creating safety concerns.

When measuring force requirements for an existing installation, a practical method is to carefully lift the object (hood, door, lid) with a bathroom scale or hanging scale to measure how much force is actually needed. This direct measurement accounts for friction in your specific installation. If it takes 35 pounds of lifting force to raise your hood all the way, you know you need a strut with a force rating close to 35 pounds.

Practical Takeaway: Write down the weight of the object the strut must support, then look for a gas strut with a force rating between 50 and 75 percent of that weight. If you can't find the weight, measure the actual force needed using a scale, and select a strut with a matching force rating.

Identifying Mounting Style and Rod Type

Gas struts attach to equipment using different mounting styles at the top and bottom, and these styles must match your equipment's design. The three most common mounting styles are ball mounts, clevis mounts, and eye mounts. Identifying which style your equipment uses is essential because a strut with incompatible mounts won't attach properly, even if all other measurements are correct.

Ball mounts consist of a metal ball attached to the strut that sits in a corresponding socket bracket on your equipment. This allows the strut to move at various angles while maintaining a secure connection. Ball mounts are common on automotive hoods and trunks because they accommodate the curved motion of