Gas spring & gas strut force calculator
Estimate the force, stroke and mounting lengths for a hinged lid, hatch or cover. Gas springs, gas struts and lift supports work the same way, so one calculation covers them all: enter the lid weight, its size and two mounting points, then read the force per gas spring in newtons and pounds-force.
How the calculation works
The calculator balances two turning moments about the hinge: the weight of the lid, which tries to close it, and the gas springs, which push it open.
It places the hinge at the origin, with the closed lid lying along the horizontal axis. When the lid has opened to an angle φ, the lid mounting point sits at A = (a·cos φ, a·sin φ). The frame mounting point does not move: B = (bx, −h), with bx negative when B is behind the hinge.
Gas springs are not constant-force parts. As the rod is pushed in, the gas is compressed and the force rises; this is called progression. P1 is the nominal force near full extension. With the lid closed the spring is compressed and typically pushes about 20–40% harder than P1, so with the recommended P1 most lids rise by themselves once unlatched. The exact ratio depends on the part, so ask us for the force points of the spring we quote. If the lid must stay shut without a latch, ask us for a lower force or a different mounting point.
The calculator also flags common geometry problems: a frame point that makes the spring shorter as the lid opens, a spring line that passes over the hinge (over-center), mounting points too close together for the stroke, and forces outside the usual range.
- Gas spring length
L(φ) = |A(φ) − B|Compressed length Lc = L(0°), extended length Lo = L(θ), stroke S = Lo − Lc. Lo = L1 and Lc = L2 in our measuring guide. - Lid moment about the hinge
M(φ) = W · g · c · cos φW is the lid mass, g = 9.81 m/s² and c the distance from the hinge to the center of gravity. M is largest with the lid closed and zero when the lid is vertical. - Lever arm of the gas spring
r(φ) = |Ax·By − Ay·Bx| / L(φ)The perpendicular distance from the hinge to the line through both mounting points. - Balance force per gas spring
F(φ) = M(φ) / (n · r(φ))The n gas springs share the load equally. - Recommended nominal force
P1 = 1.1 × F(0°)Rounded up to the next 10 N. Because of progression, the spring pushes harder than this when the lid is closed. In pounds-force: 1 lbf = 4.448 N.
The model assumes a rigid lid on a single hinge axis and measures to the centers of the end fittings. It leaves out friction, damping, temperature and the exact progression of any particular spring, so treat the result as an estimate. Horizon checks force, lengths and end fittings against your drawing or a sample before bulk production.
How to measure the mounting points
Measure with the lid closed and use the same unit for every distance.
All distances start at the pivot line of the hinge pin, not at the edge of the cabinet or the lid.
Measure along the closed lid from the hinge axis to the center of the ball stud or bracket pin. That distance is a.
Measure horizontally from the hinge axis to the center of the frame-side fitting (bx), then straight down from the hinge line (h).
Weigh the lid with its handles, glass and hardware. If heavy parts sit near the front edge, measure or estimate c instead of using half the depth.
Then check the space around the spring: the body and both end fittings need clearance from the lid and the frame in every position as the lid opens. To measure an existing gas spring, including extended and compressed length, stroke, force marking and end fittings, use the gas spring measuring guide.
An 8 kg cabinet lid on two gas springs
A cabinet lid weighs 8 kg and is 450 mm deep, hinged along its back edge. The weight is spread evenly, so the center of gravity is at mid-depth: c = 225 mm.
Two gas springs are fitted, one on each side. On each side the lid point is 200 mm from the hinge (a), and the frame point is 40 mm in front of the hinge (bx) and 110 mm below it (h). The lid opens to 90°.
Result: two gas springs of about 90 N (20.2 lbf) each, roughly 313 mm extended and 194 mm compressed, with about 118 mm of stroke. The compressed length is longer than stroke + 50 mm (168 mm), so the mounting points leave room for the spring body. These are the starting values in the calculator above.
| Step | Calculation | Result |
|---|---|---|
| Compressed length | Lc = √((200 − 40)² + 110²) | 194.2 mm |
| Extended length | Lo = √(40² + (200 + 110)²) | 312.6 mm |
| Stroke | S = 312.6 − 194.2 | 118.4 mm |
| Lever arm, closed | r = 200 × 110 ÷ 194.2 | 113.3 mm |
| Lid moment, closed | M = 8 × 9.81 × 0.225 | 17.66 N·m |
| Force per spring | F = 17.66 ÷ (2 × 0.1133) | 77.9 N |
| Recommended P1 | 1.1 × 77.9 = 85.7, rounded up | 90 N (20.2 lbf) |
Before you choose a gas spring
Use two gas springs on wide lids
A single spring on one side twists a wide lid and loads the hinges unevenly. Two springs, one on each side, share the load and keep the lid square. Set n = 2 and the force per spring halves.
Install rod-down where possible
With the rod pointing down, the oil inside keeps the rod seal lubricated, which helps the seal last and keeps end-of-stroke damping working.
Leave a little force margin
Weights and mounting positions are rarely exact, and gas spring force drops somewhat in the cold. The 10% margin in P1 covers small differences; a stronger spring makes the lid harder to close and adds load on hinges and brackets.
Keep force units straight
Gas spring force is usually marked in newtons (N), while US catalogs often list pounds-force (lbf): 1 lbf = 4.448 N, so 300 N is about 67 lbf. A force quoted in kilograms means kilogram-force: 1 kgf ≈ 9.81 N.
Most lids and covers use standard compression gas springs with matching end fittings. For cabinets, flaps and other furniture, see our cabinet gas struts; for other lengths, forces or fittings, ask about custom gas springs.
Have your force and lengths? Ask for a quote.
Send the calculator result with the quantity, both end fittings and a sketch or photo of the mounting points. We check the numbers against your application and quote a gas spring to match.