Size struts from hinge geometry and load, not a flat weight rating stamped on the box.
Gas springs for murphy beds are sized from one relationship: the supported weight, multiplied by the hinge-to-center-of-gravity distance, divided by the spring’s mounting leverage. Get that ratio right and the panel holds at any angle with light, even effort. Get it wrong and you either fight the bed shut or watch it drop on its own — no amount of picking “the next size up” off a shelf fixes a geometry problem.
Picture a full-size wall bed panel, hinged at the floor, folded up flush against a cabinet face during the day. Twice a day, in a guest room or a studio apartment, someone swings 45–70 kg (100–155 lb) of frame and mattress through 90 degrees on that hinge. The gas struts are the only thing standing between a controlled swing and a panel that either won’t budge or comes down fast. This guide covers how to size that pair correctly, and — just as important — how to tell whether your wall bed’s motion even suits a gas spring in the first place.
Is your wall bed’s motion even a pivot?
Before any force number matters, confirm the panel actually rotates about a single fixed hinge line. Gas springs are built for pivoting motion — they push against a lever arm and their effective force changes predictably as the angle changes. A design that combines rolling, sliding, or multiple linked hinges doesn’t give a gas spring a stable lever to work against, and the strut ends up over- or under-loaded at different points in the travel. This is a real, recurring design mistake — builders on furniture-construction forums have run into wall-bed concepts with too much lateral travel for a strut or linear actuator to manage cleanly, and had to fall back on a cable-and-pulley or track-based lift instead.
Suits a gas spring
Single hinge line at the base or side of the panel. The mattress deck and frame swing through a fixed arc, floor to wall, with no intermediate sliding joint. This is the standard vertical wall-bed layout, and it’s where the moment-balance math below applies directly.
Needs a different mechanism
Track-mounted or telescoping designs where the panel slides horizontally before or during the fold, or where the “hinge” point itself moves relative to the wall. Here the effective lever arm isn’t constant, and a gas spring sized for one position will be wrong at another.
The formula for sizing gas springs for murphy beds
Moment balance about the hinge:
F = (W × Lg × cos φ) ÷ (n × r)
W = supported weight (frame + mattress + hardware), Lg = hinge-to-center-of-gravity distance, φ = angle of the load arm above horizontal, n = number of struts, r = perpendicular moment arm of the strut mount.
Worked example, full-size panel: a 50 kg (110 lb) combined frame-and-mattress weight, hinge-to-CoG distance Lg of 950 mm (37.4 in), and a strut mounting geometry giving a perpendicular moment arm r of 300 mm (11.8 in), using two struts (n = 2). The worst case is the panel fully horizontal, where φ = 0° and cos φ = 1:
W = 50 kg × 9.81 = 490.5 N (110.3 lbf)
F = (490.5 N × 950 mm) ÷ (2 × 300 mm) = 776.6 N (174.6 lbf) per strut
Apply a safety-factor surcharge of roughly 1.15 for indoor furniture use (no wind or snow loading to account for, but enough margin to cover mattress variation): Fdesign ≈ 780 N × 1.15 ≈ 897 N (202 lbf) per strut. That lands inside the 150–900 N application range above — a lighter twin panel with a shorter Lg and less mass sits at the low end; a heavier queen or king panel pushes toward the top of it.
Move the mounting point — changing r — and the required force changes more than swapping to a stronger cylinder ever will. A strut mounted closer to the hinge (smaller r) needs proportionally more force for the same job; moving it further out lowers the force requirement and often smooths the feel of the lift.
Common mistake: re-specifying after a mattress swap. This shows up constantly in RV and DIY wall-bed threads — an owner upgrades to a thicker or denser mattress, the original struts “don’t seem to be helping much” anymore, and the fix people reach for is buying a strut rated for a higher weight number and hoping the mounting holes line up. That’s a guess, not a spec. The correct move is to re-run the moment balance with the new W — a heavier mattress changes the numerator directly, and the required force per strut scales with it. Two struts that were correctly matched for the old mattress can be badly under-forced for the new one, even though nothing else about the bed changed.
Gas springs for murphy beds: single strut or a matched pair?
Single strut
Reasonable only on narrow panels — typically twin-width or smaller — where the load is light enough that one centrally mounted strut won’t twist the frame off-hinge during travel. Uncommon in production wall-bed hardware for this reason.
Paired struts
Standard for full, queen, and king panels. Two struts split the load — Feach = Ftotal ÷ 2 — and must be matched within ±5% of each other from the same production batch. Mixing batches is the single most common cause of a bed that lifts unevenly.
We’ve seen this directly with a furniture-hardware OEM building fold-down guest-room beds who sourced replacement struts for a production run from two different batches when the first ran short. Nothing was wrong with either batch individually — both were within spec — but the tolerance stack between them was enough that one side of the panel consistently lifted a beat ahead of the other. Over months of daily cycling, that asymmetric load showed up as extra wear on one hinge bracket before the other. Matching both struts to the same batch and reissuing the pair solved it. It’s a detail that’s easy to miss on a bill of materials and expensive to trace once it’s in the field.
Mounting and installation notes
Mount with the rod pointing down in the closed (folded-up) position — this keeps the internal seals lubricated by the oil film and holds damping consistent over the strut’s life. Use ball-socket or eyelet end fittings that allow a few degrees of angular misalignment; a wall bed’s hinge geometry rarely holds the strut in a perfectly straight line through the full swing, and forcing a rigid connection side-loads the rod and shortens its service life. Keep both pivot points — the frame mount and the wall/cabinet mount — in the same plane of motion as the hinge itself.
For most interior installations, standard black-nitrided rod with HNBR seals is sufficient — HNBR resists the UV and ozone exposure that eventually stiffens or cracks lower-grade seal compounds, even indoors near a window. Stainless steel only earns its cost premium in genuinely humid or marine-adjacent environments — a guest cabin near open water, for instance — where standard rod finishes are more likely to see corrosion over the unit’s service life.
If the installation runs in an unheated garage conversion, cabin, or unconditioned RV, account for temperature: gas spring force drops roughly 0.3% per °C below the calibration temperature. A strut sized precisely at 20°C room temperature can feel noticeably lighter at freezing, so size with that swing in mind rather than adding raw force at the design stage.
| Bed size class | Approx. combined weight | Typical strut force (per unit, 2 struts) |
|---|---|---|
| Twin | 30–40 kg (66–88 lb) | 150–350 N (34–79 lbf) |
| Full | 40–55 kg (88–121 lb) | 350–650 N (79–146 lbf) |
| Queen | 50–65 kg (110–143 lb) | 600–900 N (135–202 lbf) |
| King | 60–75 kg (132–165 lb) | 750–900 N+ (169–202 lbf+) |
Ranges are planning-level starting points. Actual required force depends on your specific hinge-to-CoG distance and mounting geometry — run the moment balance above, or send us your dimensions.
Why source from Newtone for wall-bed hardware
Batch-matched pairs, so paired struts lift evenly from day one.
Prototype quantities and production runs sourced from the same spec, no re-qualification gap.
Sized for daily-use furniture applications, not single-use industrial duty.
Send your panel dimensions and weight; we’ll help verify the moment-balance numbers before you tool up.
Frequently asked questions
How do I choose a gas spring for a murphy bed if I don’t know the exact weight yet?
Estimate conservatively — use the heaviest mattress the bed is likely to carry, not the lightest, since re-specifying after the fact (see the mattress-upgrade note above) is the most common sizing mistake. If you’re unsure, send us the panel dimensions and we’ll help estimate a safe starting range.
Can I use one gas strut instead of two on a full or queen bed?
Not recommended. A single centrally mounted strut on a full-width panel tends to twist the frame slightly off the hinge line during travel. Paired struts, force-matched within ±5%, keep the lift symmetric.
Why does my Murphy bed feel heavier in winter?
Gas spring force drops with temperature — roughly 0.3% per °C below the temperature it was calibrated at. In an unheated space, that can be a noticeable difference between summer and winter. Spec for the coldest realistic operating temperature, not room temperature.
Do all Murphy or wall beds work with gas springs?
Only designs that rotate about a single fixed hinge line. Sliding, telescoping, or multi-joint lift mechanisms don’t give a gas spring a stable lever arm and usually need a different mechanism, such as a cable-and-counterweight or track-based system.
Should I choose stainless steel gas springs for a wall bed?
For most interior installations, standard black-nitrided rod with HNBR seals is sufficient. Stainless is worth the upgrade only in humid or marine-adjacent environments, where standard finishes are more likely to corrode over the unit’s service life.
Sizing a Murphy bed gas spring is a geometry problem before it’s a shopping decision. Confirm the panel truly pivots, run the moment balance for your actual weight and mounting layout, and match paired struts to the same batch. Everything else — rod finish, temperature range, mounting hardware — follows from there.
