How to Measure Gas Struts (for Replacement or New Installation)
Gas struts (also called gas springs) are used in a range of applications to assist with lifting, supporting, and smoothly lowering lids, panels, hatches, and doors. But whether you're replacing a strut at the end of its lifespan or fitting one for the first time, you need to make sure the size and force are appropriate for the application.
In this guide we’ll show you how to measure gas struts accurately for replacements and brand-new installations, so you can skip the trial and error and get perfect performance from day one.
Here’s what we’ll cover:
- Key measurements you’ll need
- How to measure for new struts
- Mistakes to avoid
After reading you’ll know how to ensure your strut is the right size and force.
Key Measurements You’ll Need
There’s more to measuring a gas strut than grabbing a tape measure. There are four main measurements you need to get right to ensure accuracy: **length, stroke, force, and fittings**.
Extended Length
This is the full length of the strut when it is fully extended.
How to measure: measure from the **centre of one end fitting to the centre of the other**.
Notes: if the gas strut is still in place and functioning correctly, measure it while the lid or panel is open and the strut is fully extended. If it’s been removed, check it’s not under compression before measuring.
Why it matters: getting this measurement right ensures your new strut will operate over the same distance as the original, with the correct range of motion.
Stroke Length
This is the distance the rod travels between the fully closed and fully open positions.
How to measure: **subtract the compressed length of the gas strut from its extended length**. If you only have the compressed strut to hand, carefully measure the body and visible rod length separately, then combine them for a rough estimate of the full extension.
Notes: never force a gas strut to compress for measurement.
Why it matters: the stroke determines how far the lid or panel can travel. Matching it to the original ensures the same range of motion.
Force Rating
This tells you how much lifting force the strut provides, usually shown in **Newtons** (e.g., "400N").
How to measure: look for **printed or engraved markings** on the side of the gas strut. If they’re unreadable or missing, estimate using the weight and size of the lid.
Notes: the force must be matched to your application. If the strut is too weak, the lid won’t stay open. If it’s too strong, it may be hard to close or place strain on the hinges.
Why it matters: getting the force right is critical for safe, effective operation.
End Fittings
These are the components at each end of the strut that connect it to your lid or frame.
How to measure: identify the fitting type, commonly ball sockets, clevis forks, eyelets, or threaded ends, and take note of their dimensions. For ball sockets, measure the ball diameter (typically 6mm, 8mm, or 10mm). For other fittings, check pin or hole diameters.
Notes: pay attention to the angle or offset of the fittings, especially if your strut operates in a confined space.
Why it matters: choosing the correct end fittings ensures a secure connection and proper alignment within your application.
How to Measure for New Gas Struts (When None Are Installed)
If you’re building something from scratch or adding struts to a lid or door that doesn’t yet have them, the process is slightly more involved. But with a bit of planning and the right knowledge it doesn’t need to be stressful!
Here’s how to do it.
- Measure the Lid
Start by measuring the height (or depth) of the lid or panel you want to support. You’ll also need to know its **approximate weight**. If you’re not sure, estimate or weigh it on a bathroom scale.
Knowing the weight and size helps determine both the correct strut length and the amount of force required. - Decide How Far You Want It to Open
Think about how far you want the lid or panel to open. A typical range is between **70° and 110°**, depending on the application. Mark this open angle with masking tape or a propped-up lid, if possible, then measure the distances from hinge to proposed mounting points.
This helps identify the extended length and mounting geometry needed for smooth operation. - Estimate Mounting Positions
A general rule of thumb is to place the body end of the strut about **one-third of the way along the lid from the hinge**, and the rod end about **one-third of the way down the side wall or frame**. This varies by project but provides a good starting point.
Once you have rough measurements and force estimates, you can plug them into an online sizing calculator, designing service or send them to a supplier for help choosing the right strut.
Common Mistakes to Avoid
Even a few millimetres can make a difference when it comes to gas struts. Here are the most common pitfalls to be aware of before you start work:
- **Avoid measuring only the body or rod:** always measure from **centre-to-centre of fittings**.
- **Avoid guessing the force rating:** use known weights or ask for help if the rating isn’t visible.
- **Avoid ignoring end fittings:** make sure new struts match or are compatible with existing hardware.
- **Avoid replacing just one strut:** always **replace in pairs** for safe, balanced performance.
- **Avoid choosing the wrong mounting geometry:** this can limit motion or stress the hinges.
Whether you’re replacing a gas strut or fitting one for the first time, taking **accurate measurements** paves the way for success and avoids frustration. By checking the extended length, stroke, force rating and fittings, you can avoid mistakes and enjoy smooth, reliable lift and support for years to come.
For help selecting the right strut or to learn more, don’t forget to check out our guides:
You can also explore our full range or contact our support team for tailored advice.