How Much Force Does Your Linear Actuator Actually Need? Angles, Levers, and Real Weight
Most actuator sizing mistakes do not come from picking the wrong product. They come from answering the wrong question. Buyers ask, "How heavy is the thing I want to move?" and then buy an actuator rated for that weight. But an actuator almost never lifts its load straight up, dead vertical, with the load sitting on top of it. It pushes at an angle, through a hinge, with leverage working for or against it. The force the actuator actually feels can be far larger — or far smaller — than the weight on the scale.
This guide shows how to calculate the real number, with a worked example you can adapt to your own project.
Why the Weight on the Scale Is Not the Answer
Three things stand between the weight you measure and the force your actuator must deliver:
- Angle. An actuator pushing at a shallow angle to the moving part wastes most of its force sideways. Only the component of force perpendicular to the moving arm does the lifting. The shallower the angle, the more force you need for the same lift.
- Leverage. Where the actuator attaches matters as much as how strong it is. An actuator mounted close to the hinge has to push much harder than one mounted further out, because it has a shorter lever arm than the load does.
- Friction and reality. Hinges bind, seals drag, linkages rub, and loads are rarely perfectly balanced. The calculation gives you the ideal number; the real mechanism always asks for a little more.
None of this requires engineering software. It requires a tape measure, a scale, and one formula.
The Three Things to Measure First
1. The real weight. Weigh the moving part, or measure its weight with a luggage scale at the point where the actuator will push. Do not estimate from the product brochure, and do not weigh only the panel while forgetting what is mounted on it — a hatch plus its motor, lining, and contents is the load, not the bare hatch. If you cannot weigh it, you cannot size for it; guessing here is the single most common cause of an undersized actuator.
2. The geometry. Measure two distances from the hinge (the pivot the moving part rotates around):
- The distance from the hinge to the load's centre of gravity — call it the load arm.
- The distance from the hinge to the actuator's moving mounting point — call it the actuator arm.
Also note the angle between the actuator and the moving part at the start of the lift. That is usually the worst position: the part is at its lowest, the angle is at its shallowest, and gravity has its longest lever. Size for the worst position, not the comfortable middle of the travel.
3. The direction. Is the actuator pushing, pulling, or both at different points in the travel? Push and pull ratings are not automatically equal — check the product page for both if your job pulls. And is the load purely the moving part, or does wind, snow, or a person leaning on it add force? Size for the loads the mechanism will actually see, and do not size for loads it was never designed for (see the FAQ).
The Calculation: One Formula, Worked Example
For a hinged panel, hatch, or lid, the required actuator force is:
F = (W × load arm) ÷ (actuator arm × sin θ)
Where:
- F is the actuator force you need
- W is the weight of the moving part (in newtons; multiply kilograms by 9.81, or roughly by 10 for a quick estimate)
- load arm is the hinge-to-centre-of-gravity distance
- actuator arm is the hinge-to-actuator-mount distance
- θ is the angle between the actuator and the moving part
Worked example (illustrative numbers, not a product specification)
Suppose a hatch weighs 20 kg, so W ≈ 200 N. Its centre of gravity sits 0.6 m from the hinge, and the actuator mounts 0.3 m from the hinge.
- At a healthy 60° angle (sin 60° ≈ 0.87): F = (200 × 0.6) ÷ (0.3 × 0.87) = 120 ÷ 0.26 ≈ 460 N.
- At a shallow 30° angle (sin 30° = 0.5): F = 120 ÷ (0.3 × 0.5) = 120 ÷ 0.15 = 800 N.
The same hatch, the same weight — but nearly twice the force, just because the starting angle is shallower. This is why two people with the "same" project can need very different actuators: their mounting geometry is different.
Two lessons fall out of the example. First, moving the actuator mount further from the hinge is often cheaper than buying a stronger actuator — doubling the actuator arm halves the required force. Second, check the whole travel, not just one position: if the angle gets shallower at either end of the stroke, calculate there too, and size for the largest result.
For a straight vertical lift with no hinge — a platform rising on guides, for example — the geometry simplifies: the actuator carries the weight directly, so the required force is the weight plus friction in the guides. For a scissor or multi-link mechanism, the geometry is more complex than this single-hinge formula; in that case, measure the worst position carefully, and consider asking the mechanism's maker for its force curve rather than extrapolating from one formula.
From Calculated Force to a Model: Take the Next Rating Up
Once you have your worst-case number, do not buy the actuator rated exactly at that number. Friction, wear, temperature, and the odd extra load all push the real requirement above the ideal calculation. The practical rule is simple: choose the next force rating above your worst-case result. That margin is your insurance against everything the formula could not see.
For reference, HyHaven's force range runs from the U5 at 500N through the U1 at 900N, the U2 at 1500N, the U11 at 3500N, the U3 at 6000N, and the U6 at 7000N, up to the 508 at 12000N. If your worst case comes out at, say, 800 N, the next rating up is the right conversation to have — not the 800 N actuator that does not exist, and not the 12000N unit that would demand a far larger power supply for no benefit.
That last point matters: a far stronger actuator is not a free upgrade. It draws more current — see the full-load current table in our power supply sizing guide — and it can overpower a mechanism designed for a lighter part. Size up one step, not five.
Also remember that force and speed trade against each other: in general, a higher-force gearing moves more slowly. If your project needs both high force and fast movement, that combination deserves a second look before ordering — check the speed on the product page's Full Specifications for the exact model, and do not assume two models share a speed because they share a voltage.
Dynamic Load, Static Load, and Loads You Should Not Size For
Dynamic load is the force while the part is moving. Static load is the force while it is holding still. A hatch held open by its actuator is a static load; the same hatch being lifted is a dynamic load. Size for the moving case first — that is where the angle and leverage penalties bite — and then confirm the holding case on the product page.
Do not size for abuse loads: a person standing on the platform, a gust slamming the hatch, or the actuator stalling against a hard stop at the end of travel. Those are not sizing cases; they are design problems. A mechanism that routinely stalls its actuator against a hard stop will kill the actuator regardless of rating — the built-in limit switch stops the motor at the ends of its own stroke, but it cannot protect a mechanism that jams mid-travel. Our limit switch guide and troubleshooting checklist cover both points.
One more trap: side load. This entire calculation assumes the actuator pushes and pulls in a straight line. If the mechanism forces the rod sideways — a misaligned bracket, a binding hinge, a platform that racks — the real force on the mechanism is higher than calculated, and the actuator wears in ways no rating covers. Fix the alignment; do not buy a bigger actuator to overpower it. Our stroke measurement guide pairs with this article: stroke decides whether the travel fits, force decides whether the lift works.
Common Sizing Mistakes
| Mistake | Why it fails | What to do instead |
|---|---|---|
| Buying for the scale weight only | Ignores angle and leverage | Use the moment formula at the worst position |
| Calculating only at mid-travel | The start position is usually worst | Calculate at the shallowest angle in the travel |
| Mounting close to the hinge, then upsizing | Short lever arm demands huge force | Move the mount out first, then re-calculate |
| Assuming pull rating equals push rating | They are not automatically equal | Check both on the product page |
| Buying far stronger "to be safe" | Bigger supply, more current, overpowered mechanism | Take the next rating up, not five |
| Sizing for a person standing on it | That is not a normal load case | Redesign the mechanism; do not oversize past it |
| Ignoring friction and binding | Real mechanisms always add drag | The next-rating-up margin absorbs it — barely, so keep the mechanism free |
FAQ
Can I just buy the strongest actuator and be done with it?
You can, but you will pay for it twice: once in the price, and again in the power supply and controller, which must handle a much larger full-load current. And a far stronger actuator can damage a light mechanism. The next rating up is the safe choice, not the maximum.
My calculation says 450 N. Is a 500N actuator enough?
If 450 N is genuinely your worst case — shallowest angle, full weight, friction considered — then the next rating up covers it. If 450 N was calculated at a comfortable mid-travel angle, re-calculate at the start position first; the worst case is the number that counts.
What if my mechanism is a scissor lift or four-bar linkage?
The single-hinge formula does not capture multi-link geometry. Measure the worst position, and if the mechanism maker publishes a force curve, use it. Do not extrapolate a single-hinge result across a linkage and call it a calculation.
Does a 24V actuator push harder than the same model in 12V?
Not by virtue of voltage. Force is a property of the model and its gearing; voltage changes the current draw, not the force rating. Compare models by their rated force on the product page, not by their voltage.
Why did my actuator work on the bench but stall on the job?
On the bench it carried no load at a friendly angle. On the job it meets the real angle, the real weight, and the real friction — exactly the three things this guide asks you to measure. Re-measure the installed geometry; the bench test was never the sizing test.
I already bought an actuator and it stalls. Is the calculation still useful?
Yes — run it now. If the calculation says the actuator is undersized, no wiring change will fix it. If the calculation says it should be enough, the fault is elsewhere: binding, alignment, or an undersized supply. The troubleshooting checklist walks that second path.
Measure the weight, measure the geometry, calculate at the worst position, and take the next rating up. If you want a second pair of eyes on the numbers, start from our linear actuator selection guide — and if the calculation points between two models, the stronger of the two is the one to check first, not the cheaper one.