Gas Spring Sizes, How to Measure & Choose the Right Gas Strut
A practical guide to stroke length, force ratings, and end fittings, so you order the right part first time.
The Three Key Gas Strut Measurements
Every gas spring is defined by these three dimensions. Get all three before ordering.
Measurement 1
Stroke Length
Extended length minus compressed length, the distance the rod travels. This is the “size” most people refer to when they say a gas strut is “300mm” or “400mm”. Measure the old strut fully open and fully closed; the difference is the stroke. Common vehicle strut sizes: 150mm to 500mm stroke.
Measurement 2
Compressed Length
Total length of the strut when the panel is fully closed, measured end fitting to end fitting. This determines whether the strut fits in the available mounting space. A strut with a 400mm stroke will have a compressed length of approximately 430 to 500mm depending on end fitting type.
Measurement 3
Extended Length
Total length of the strut when fully open, measured end fitting to end fitting. This determines the maximum opening angle of the panel. Extended length equals compressed length plus stroke length. A mismatch here means the panel either won’t open far enough or over-extends the strut.
Understanding Force Ratings (Newtons)
Force rating, measured in Newtons (N), is the upward push the strut exerts. It is independent of stroke length. Two struts with identical dimensions can have completely different force ratings.
A rough conversion: 100N is approximately 10kg of lift force. So a 300N strut provides approximately 30kg of support force, but the actual panel weight it can hold depends on the distance from the hinge to the strut mounting point.
Common force rating ranges by application:
- Canopy gas struts (bakkie canopy): 200N to 600N depending on canopy weight and load
- Boot lid gas struts: 200N to 400N depending on vehicle make and lid weight
- Bonnet gas struts: 150N to 300N depending on bonnet weight
- Industrial / commercial applications: highly variable, specify by application
Always match or slightly exceed the original force rating. Under-rating means the panel drops. Over-rating means the panel opens too forcefully and strains the hinges.
Standard Gas Strut Size Reference
Common stroke lengths and their typical vehicle applications. Force rating is specified separately, call us to confirm the correct rating for your application.
| Stroke Length | Approx Compressed Length | Typical Applications | Common Force Range |
|---|---|---|---|
| 150 – 200mm | 180 – 250mm | Bonnet supports, hatchback supports, small cabinet lids | 100 – 300N |
| 250 – 300mm | 290 – 370mm | Boot lids (sedan and hatchback), medium canopy applications | 150 – 400N |
| 350 – 400mm | 400 – 490mm | Large canopy lids, SUV boot lids, enclosed trailer lids, toolbox lids | 200 – 700N |
| 450 – 500mm | 510 – 610mm | Heavy canopy applications, trailer ramp doors, industrial panels | 300 – 800N |
| 550 – 800mm | 620 – 950mm | Large industrial panels, medical equipment, commercial lids | 400 – 1500N |
All measurements are approximate. Actual dimensions vary by manufacturer and end fitting type. Call us to confirm dimensions for your specific application.
Rod Diameter and Body Diameter
Diameter affects load capacity and durability. Larger-diameter struts handle heavier loads and longer service lives. Most vehicle applications use standard small-diameter struts, industrial applications may require larger sizes.
Rod Diameter (piston rod)
- 6mm, light vehicle and domestic applications
- 8mm, standard vehicle applications (most common)
- 10mm, heavier vehicle and light industrial
- 14mm+, heavy industrial applications
Body Diameter (cylinder)
- 15mm, light vehicle (bonnet, small boot lids)
- 18 – 22mm, standard vehicle (most common)
- 22 – 28mm, heavy canopy and light industrial
- 28mm+, heavy industrial (regassing may be viable)
End Fitting Types
The end fitting connects the strut to its mounting point. The most common types are ball socket ends (snap onto a ball stud, standard on vehicles), clevis/fork ends (bolt-through mounting, industrial use), and eye bolt ends (loop mounting, lighter applications).
How to Order the Right Gas Strut Size
Gas struts, also called gas springs, are specified by stroke length, compressed length, and force rating in Newtons. Once you have these three values, ordering the right unit is straightforward.
Step 1, Measure the old strut. Note the compressed length, extended length, and stroke length (extended minus compressed).
Step 2, Find the force rating. It’s printed on the cylinder body (e.g. “300N” or “F 450”). If it’s unreadable or the strut has fully failed, give us the panel weight and hinge geometry and we’ll calculate it.
Step 3, Call or WhatsApp us. We confirm the correct specification from stock and dispatch same day. Don’t guess on force rating, a wrong rating means the panel drops or over-extends the strut.
✆ Call +27 71 080 5429Frequently Asked Questions
Common questions about gas spring sizes and how to measure gas struts.
How do I measure a gas strut?
Measure in three dimensions: compressed length (fully closed, end fitting to end fitting), extended length (fully open, end fitting to end fitting), and stroke (extended minus compressed). Also note the force rating printed on the cylinder body. If the old strut has failed completely, measure the mounting point positions with the panel at its intended open angle.
What does the force rating mean on a gas strut?
Force rating in Newtons (N) is the upward push the strut exerts. 100N equals approximately 10kg of lift force. The correct force rating depends on the panel weight and the distance from the hinge to the strut mounting point. Always match the original force rating when replacing a strut.
Can I use a different length gas strut if I can’t find my exact size?
Sometimes, but only with careful calculation. A different stroke length changes the opening angle of the panel and may stress the hinge or over-extend the strut at full open. Call us with your measurements and we’ll tell you whether a substitute size is safe for your application.
What is the difference between a gas spring and a gas strut?
They are the same product, gas spring is the engineering/industrial terminology; gas strut is the more common vehicle repair term. Both refer to the nitrogen-filled cylinder that holds panels open and controls their movement. You may also hear them called gas stays, gas lifts, or gas holders.
How many Newtons do I need for my boot lid?
Most vehicle boot lids require between 200N and 400N per strut (two struts typically fitted). The correct rating depends on your specific vehicle model. Call or WhatsApp us with your vehicle year, make, and model, we specify by vehicle, so you don’t need to calculate the force yourself.
Need a Gas Strut? Call Us Today.
We specify by vehicle and application, you don’t need to calculate force ratings or look up strut sizes. Tell us what vehicle and what panel, and we’ll sort the rest.