How to determine the length and strength of a gas strut replacement

If you need to replace your existing gas struts, below is an explanation on how to calculate the size and force (Nm) needed.

If you are unsure of how to measure your existing gas struts, please see our page on How to Measure Gas Struts.

At Fineline Fabrications we typically see people needing gas struts for three reasons:

  • Replacing old struts that have lost their force
  • Swapping out struts for ones with a greater lifting force
  • Introducing Gas Struts to something


Replacing old struts is easy, all we need to know is the diameter of the shaft, the diameter of the cylinder and the original newtons or pounds of force.

Swapping out struts for ones with greater lifting force is also easy. This is usually needed when something has been added like solar panels or roof racks and the original struts can’t handle the extra load. When swapping out struts for stronger versions all we need to know is the diameter of the shaft, the diameter of the cylinder, original newtons of force and how much extra weight you have added.

When adding struts for the first time you need to follow our Gas Strut Selection Formula:

  • Calculate half the dimension of what you are lifting (H),
  • Weight of what you are lifting (G),
  • Mounting distance from the hinge (L)
  • What size struts you require.

 (Please see our formula below at the bottom of this article. Simply replace H, G and L in our formula to calculate the Nm of force required.)

What is the size of the door you are lifting? For the purpose of this article, we will say we have a door with a 1000mm drop, this means (H) would equal 500.

You need to weigh what you are lifting, the easiest way to do this is with a broomstick and bathroom scales. Ideally, you want to weigh a door roughly halfway along as this is a closer indication of true weight the gas struts will be lifting. If you can’t weigh a door halfway along, at the end is fine but you should double this weight as the force to lift gets harder as you move closer to the hinge point. For the purpose of this article, we will say our door weighs 5 kilograms. One kilogram equals 10 newtons, so a 5-kilogram door means that (G) equals 50.

Mounting distance from hinge:
Gas struts should be fitted roughly 20% from the hinge, so once again if our door has a 1000mm drop, 20% from hinge point would be 200.

What size struts you require:
The size of the strut is determined by the door drop. At Fineline Fabrications we suggest a strut near 55% of the door drop, so if you have a 1000mm door drop a 550mm gas strut would be ideal.

Fineline Fabrications stock a wide range of gas struts. All available sizes can be found here. 


How to Calculate a Gas Strut