How to calculate what Gas Struts you require

gas strut how to image
gas strut formula

Gas struts can be very dangerous, believe it or not, there was a workplace death involving a faulty gas strut. If you are unsure of what you are doing you should always get help from a professional. If you are attempting to install your own gas struts please firstly visit work safe.

At Dunn & Watson 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.


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:

At Dunn & Watson we suggest a strut near 60% of the door drop, so if we have a 1000mm door drop our 595mm gas struts are ideal.

When all the data is entered into the gas strut selection formula, we get 72 newtons. At Dunn and Watson we stock 100 newtons in a 595mm range, these would be ideal.

As mentioned earlier gas strut installation should only be performed by a professional and workplace safety should always be at the forefront of your mind when handling gas struts.

Dunn & Watson stock a huge range of gas struts for sale, and all sizes.