Gas Strut Force Calculator

Accurately determine the required force for your hinged lid, hatch, or door.

Calculation Results

Chart visualizing total force vs. force required per strut.

What is a Gas Strut Calculator?

A Gas Strut Calculator is a specialized tool designed to determine the necessary force (measured in Newtons or pounds-force) for a gas strut to safely and effectively lift and hold open a hinged lid, door, or hatch. Anyone from DIY enthusiasts building a custom toy box to engineers designing engine bay hoods can use this calculator to find the right strut for their project, preventing the lid from being too heavy to lift or slamming shut unexpectedly. A common misunderstanding is that any gas strut will work for any lid; however, the force must be matched precisely to the lid’s weight and geometry to ensure proper function and safety.

Gas Strut Calculator Formula and Explanation

The calculation is based on the principle of torques, where the lifting force of the gas strut must overcome the force of gravity acting on the lid’s weight. A simplified but effective formula used by this calculator is:

Total Force (N) = [ (Lid Weight [kg] * 9.81 * (Lid Length [mm] / 2)) / Lid Mounting Point [mm] ] * 1.15

The formula calculates the torque created by the lid’s weight (acting at its center of gravity, assumed to be L/2) and then determines the force the strut needs to exert at its specific mounting point to counteract that torque. A 15% safety factor (multiplying by 1.15) is added to account for variations in temperature, manufacturing tolerances, and hinge friction.

Variables used in the gas strut force calculation.

Variable	Meaning	Unit (Metric / Imperial)	Typical Range
F	Force per Strut	Newtons (N) / Pounds-force (lbf)	50 – 2500
W	Lid Weight	Kilograms (kg) / Pounds (lbs)	2 – 100 / 4 – 220
L	Lid Length	Millimeters (mm) / Inches (in)	300 – 2000 / 12 – 80
M	Mounting Point Distance	Millimeters (mm) / Inches (in)	50 – 500 / 2 – 20

Practical Examples

Example 1: Wooden Toy Box Lid

Imagine you have a wooden toy box with a lid that needs support.

• Inputs:
  • Lid Weight: 8 kg
  • Lid Length: 700 mm
  • Mounting Point: 180 mm from hinge
  • Number of Struts: 2
• Results: The calculator would determine a total required force of approximately 219 N, meaning each of the two struts should be rated for around 110 N.

Example 2: Steel Toolbox Hatch

Consider a heavy-duty steel hatch on a utility vehicle.

• Inputs:
  • Lid Weight: 45 lbs
  • Lid Length: 36 inches
  • Mounting Point: 10 inches from hinge
  • Number of Struts: 2
• Results: Using the Imperial system, the tool calculates a total force of 185 lbf, requiring two struts of about 93 lbf each.

How to Use This Gas Strut Calculator

1. Select Units: Start by choosing either the Metric (kg/mm) or Imperial (lbs/in) system to match your measurements.
2. Enter Lid Weight: Accurately weigh the lid or hatch and enter this value. This is the most critical input.
3. Enter Lid Length: Measure from the center of the hinge to the outermost edge of the lid.
4. Enter Mounting Point: Decide where on the lid (measured from the hinge center) the strut will be attached. A common rule of thumb is to place it at about 20-25% of the lid’s total length.
5. Select Number of Struts: Choose whether you will use one or two struts. Two is recommended for stability on wider lids.
6. Interpret Results: The calculator provides the force required for each strut, the total combined force, and the “effective weight” the struts will be lifting. Always choose a strut with a force rating equal to or slightly higher than the calculated value.

Key Factors That Affect Gas Strut Calculation

• Lid Weight: The heavier the lid, the more force is required. This is the most significant factor.
• Lid Length: A longer lid creates more leverage for gravity, increasing the required strut force, assuming the mounting point stays the same.
• Mounting Geometry: Moving the strut’s mounting point on the lid closer to the hinge dramatically increases the force needed. Moving it further away reduces the required force. This is a critical adjustment point.
• Opening Angle: While this simple calculator assumes a standard opening, the force required from a strut can change as the angle of the lid changes. For a detailed analysis, you might need a more advanced hinge force calculator.
• Temperature: Gas struts are filled with nitrogen gas, which expands when hot and contracts when cold. A strut will be stronger on a hot day and weaker on a cold day. The built-in safety factor helps compensate for this.
• Number of Struts: Using two struts cuts the force requirement for each individual strut in half, providing better balance and stability.

Frequently Asked Questions (FAQ)

1. What happens if my gas strut is too strong?

A strut with excessive force will make the lid difficult to close and may cause it to fly open too quickly. It can also put stress on the hinges and mounting points.

2. What if the strut is too weak?

A weak strut will not be able to lift the lid on its own and, more dangerously, will not be able to hold it open, creating a risk of it slamming shut.

3. Where is the best place to mount a gas strut?

A general guideline is to mount the strut’s moving end at 20-25% of the lid’s length away from the hinge. For a 1000mm lid, this would be 200-250mm. This provides good leverage without requiring excessive force. Consider using a strut length calculator for more specific guidance.

4. How do I measure the lid weight accurately?

For smaller lids, use a bathroom scale. For larger doors, you can use the scale to measure yourself, then measure yourself holding the unhinged door, and find the difference.

5. Do I need one or two gas struts?

For any lid wider than about 600mm (24 inches), it is highly recommended to use two struts to prevent the lid from twisting and to ensure even lifting force.

6. Why is there a safety margin in the calculation?

The safety margin (typically 10-20%) accounts for factors like hinge friction, slight inaccuracies in measurement, and the effect of temperature on the strut’s gas pressure.

7. What is the difference between Newtons (N) and pounds-force (lbf)?

Newtons are the metric unit of force, while pounds-force is the imperial equivalent. They are both measurements of force, not mass. 1 lbf is roughly equal to 4.45 N. Our force conversion calculator can help with this.

8. Should the strut be mounted rod up or rod down?

Gas struts should always be installed with the cylinder (the thicker part) at the top and the rod (the thinner, moving part) at the bottom. This ensures the internal seals remain lubricated by the oil inside the strut, extending its lifespan.