Gas Strut Calculator
Calculate the precise force and length requirements for your gas struts
Calculate Your Gas Strut Specifications
Your Gas Strut Specifications
What Are Gas Struts?
Gas struts, also known as gas springs or gas dampers, are sealed units filled with compressed nitrogen gas. They provide controlled force to assist in opening and holding doors, lids, bonnets, tailgates, and hatches. The internal pressure creates an extending force that counteracts the weight of the application, making heavy items easier to lift and preventing them from slamming shut.
Force Rating
Measured in Newtons (N), this indicates the force the strut exerts when extending. Higher ratings support heavier applications.
Stroke Length
The distance the piston rod travels from fully compressed to fully extended. Critical for determining mounting positions.
Extended Length
Total length when fully extended, measured from centre of one mounting point to centre of the other.
End Fittings
Connection points vary by application: ball joints, eyelets, clevis brackets, or threaded studs.
How to Select the Right Gas Strut
Step 1: Measure Your Application
Accurately weigh your door, lid, or hatch including all hardware and fittings. Measure the height from the hinge pivot point to the furthest edge. Identify where the strut will mount on both the fixed frame and moving component.
Step 2: Calculate Required Force
The force needed depends on the weight, mounting position, and opening angle. The torque created by the weight must be counteracted by the strut force. Mounting the strut further from the hinge reduces the force required, but may affect the opening angle and available space.
Step 3: Determine Strut Length
The extended length should typically be 55-65% of the door height for optimal performance. This ratio provides good leverage whilst preventing over-extension. The mounting geometry must allow the strut to compress without bottoming out when the door closes.
Step 4: Check Mounting Angles
Gas struts work most efficiently when mounted at angles between 30° and 60° to the door surface when closed. Steeper angles provide greater initial lift force but reduce holding power at full extension. Shallower angles offer better support when open but may struggle with initial lifting.
Common Applications
- Vehicle bonnets and tailgates for cars, vans, and lorries
- Campervan and caravan overhead cabinets and storage lockers
- Toolbox lids and equipment cases
- Kitchen cabinet doors and appliance lids
- Industrial machinery guards and access panels
- Furniture such as ottoman storage beds and lift-up desks
- Boat hatches and marine equipment covers
- Agricultural equipment access doors
Installation Guidelines
Mounting Position
Mark the mounting points before drilling. The lower mount attaches to the fixed frame, typically positioned near the hinge but offset to create the working angle. The upper mount fixes to the moving component at a distance that allows full compression when closed and full extension when open.
Installation Procedure
Fit the lower mounting first with the strut in its compressed state. Close the door slowly to verify that the geometry allows full closure without over-compressing the strut. If interference occurs, adjust the upper mounting point. Test the operation several times before final tightening. Always install gas struts with the piston rod pointing downward when extended to prevent internal seal contamination.
Maintenance
Clean the piston rod periodically with a soft cloth and mild detergent. Avoid abrasive cleaners that might damage the chrome plating. Check mounting bolts for tightness every six months in high-use applications. Lubricate end fittings with a light machine oil if they become stiff. Replace struts that have lost pressure, typically indicated by the door dropping or requiring manual support.
Frequently Asked Questions
How do I know what force rating I need?
Use the calculator above by entering your door weight, dimensions, and mounting position. As a rough guide, a 5kg door typically requires 50-80N per strut depending on geometry. Heavier doors or those opening to vertical positions need proportionally more force. When in doubt, select the next size up.
Can I use one strut instead of two?
Whilst technically possible, two struts provide better stability and weight distribution. A single strut must mount on the centreline of the door, which is often impractical. Two struts also prevent twisting and provide redundancy if one fails. Only use a single strut for narrow, lightweight applications under 3kg.
What happens if the strut is too strong?
An over-specified strut will cause the door to spring open forcefully and may make closing difficult. It can stress hinges and mounting points. However, a modest surplus (10-20%) is beneficial for longevity and accounts for pressure loss over time. If the strut is significantly too strong, replace it with a lower force rating.
What happens if the strut is too weak?
An under-specified strut will fail to support the door’s weight, requiring manual assistance to open and potentially allowing the door to drop unexpectedly. This creates a safety hazard and puts excessive strain on the strut, leading to premature failure. Always choose adequate force ratings.
How long do gas struts last?
Quality gas struts typically last 40,000 to 60,000 cycles under normal conditions. This translates to 5-10 years for most applications. Harsh environments, extreme temperatures, or mounting with the rod upward can reduce lifespan. Signs of wear include slower extension, oil leakage, or loss of holding force.
Can gas struts be used outdoors?
Yes, but select marine-grade or stainless steel models for outdoor or corrosive environments. Standard chrome-plated struts will corrode in coastal areas or when exposed to road salt. UV-resistant seals are essential for applications with direct sun exposure. Temperature extremes affect gas pressure, so compensate by selecting slightly higher force ratings for cold climates.
Can I adjust the force of a gas strut?
No, the force rating is fixed by the internal gas pressure and cannot be adjusted in the field. If the force is incorrect, you must replace the strut with one of a different rating. Some manufacturers offer custom pressures for special applications, but standard struts come in fixed increments typically ranging from 50N to 1000N.
What is the difference between gas struts and gas springs?
The terms are interchangeable and refer to the same product. “Gas strut” is more common in British English, whilst “gas spring” is often used in technical documentation. Both describe a sealed cylinder containing compressed gas that provides a linear extending force. Dampers are similar but designed to resist motion in both directions.
Technical Considerations
Temperature Effects
Gas strut force varies with temperature due to the ideal gas law. Force increases approximately 3% per 10°C rise. Applications operating in extreme cold may need 15-20% higher force ratings to compensate for reduced gas pressure. Conversely, high-temperature environments like engine compartments require heat-resistant seals rated to 80°C or above.
Mounting Orientation
Always mount gas struts with the piston rod facing downward when extended. This orientation keeps the internal lubrication around the seals and prevents dry operation. Inverted mounting causes premature seal wear and may void warranties. If your application requires upward-facing rods, specify special orientation struts with modified seals.
End Fitting Selection
Ball and socket fittings allow angular movement and are ideal for most applications. They accommodate slight misalignment and binding-free operation through the full stroke. Eyelet fittings are more robust for high-load applications but require precise alignment. Clevis brackets provide adjustability during installation but add complexity.
Stroke vs Extended Length
The stroke (compression distance) is typically 30-40% of the extended length. A 500mm strut usually has a 150-200mm stroke. The compressed length equals the extended length minus the stroke. Verify that your mounting geometry provides clearance for the full compressed length plus any mounting bracket dimensions.