Choosing a linear actuator is not just a matter of matching the actuator’s force rating to the weight of the load. Mounting angle, leverage, stroke length, friction, side loading, speed, duty cycle, and power supply capacity all affect whether the actuator will move reliably. This blog explains simplified calculations for estimating actuator force and stroke length in two common situations: straight-line motion and hinged rotary motion. Use these calculations as a reference for your starting point, then verify your final selection with the product datasheet or the Linear Actuator Calculator.
What Parameters Do You Need Before Choosing an Actuator?
Before calculating actuator force or stroke, collect the basic application details.
| Parameter | What to Measure or Confirm | Why It Matters |
|---|---|---|
| Load weight | Weight of the object being moved | Starting point for force calculation |
| Motion type | Linear lift, slide, door, hatch, trapdoor or tilt | Determines the calculation method |
| Mounting points | Rear and front actuator mount locations | Affects leverage, force and fit |
| Stroke length | Actuator extension distance | Determines travel range |
| Voltage/current | System voltage and available current | Ensures electrical compatibility |
| Duty cycle | Run/rest pattern | Prevents overheating |
| Controls | Switch, relay, remote, feedback, or synchronized control | Determines wiring and compatibility |
Linear Actuator Force Calculation for Straight-Line Motion
Straight-line motion includes lifts, slides, and vertical motion where the load moves along a defined path. Even in these applications, actuator angle matters.
If the actuator is mounted vertically and pushes directly in line with the load, the required force is close to the load weight plus friction and safety margin. If the actuator is mounted at an angle, only part of its force contributes to vertical movement.
Step 1: Calculate Stroke Length
Stroke length is the difference between the actuator’s fully extended and fully retracted length:
Stroke = Extended actuator length - Retracted actuator length
For angled mounting, measure the distance between the two mounting points at both the start and end positions. The difference is the required stroke. For more detail, review the Linear Actuator Stroke Length Guide.
Step 2: Calculate Required Force
For a simple angled vertical lift, the useful lifting force is the vertical component of the actuator force. A simplified relationship is:
Required actuator force = Load force / sin(actuator angle)
The actuator angle is measured between the actuator and the direction of useful motion. As the angle gets smaller, required actuator force increases.
Step 3: Add Safety Margin
After estimating force, add margin for real-world conditions such as friction, binding, seal compression, wind, rain, snow, debris, uneven loading, startup force, and wear over time.
Do not oversize blindly. A higher force actuator may draw more current, move at a different speed, require stronger mounting brackets, or place more stress on the structure.
Rotary Motion: Doors, Hatches and Trapdoors
Rotary motion occurs when the load pivots around a hinge, such as a door, hatch, lid, trapdoor, solar panel, or dump bed. In these systems, the actuator must overcome torque around the hinge.
Torque = Force x Distance from hinge
A door is easier to open when force is applied farther from the hinge because the lever arm is longer. The same principle applies to actuator mounting. Mounting the actuator too close to the hinge usually reduces stroke length but increases required force.
Stroke Length for Hinged Motion
For hinged motion, stroke is still the fully extended actuator length minus the fully retracted actuator length. Measure the distance between the actuator mounting points in the closed position and again in the open position. The difference between those two distances is the required stroke.
Force and Torque for Hinged Motion
For hinged doors and hatches, calculate force at both the starting and ending positions. Depending on the mounting geometry, the highest force may occur when the hatch is closed, partially open, or fully extended.
- Estimate the load torque around the hinge.
- Estimate the actuator’s effective lever arm.
- Divide the torque by the actuator lever arm.
- Adjust for actuator angle.
- Add a safety margin.
- Verify stroke, retracted length, and extended length.
For more torque-specific guidance, read the Linear Actuator Torque Calculation Guide.
Common Sizing Mistakes
| Mistake | Why It Causes Problems | Better Approach |
|---|---|---|
| Matching actuator force only to load weight | Ignores angle, leverage and friction | Calculate force from geometry |
| Ignoring stroke vs travel difference | Load movement may not equal actuator stroke | Measure mounting distance at both endpoints |
| Mounting too close to a hinge | Creates poor leverage and high force demand | Test alternate mounting points |
| Allowing side loading | Can bend the rod or shorten actuator life | Let guides and structure carry side loads |
| Ignoring duty cycle | Repeated operation can overheat the actuator | Check datasheet duty cycle and operate within ratings |
| Current draw oversight | Power supply or switch may be undersized | Verify voltage, current and fuse requirements |
Use the Linear Actuator Calculator
The Progressive Automations Linear Actuator Calculator can help estimate force, speed, angle and length requirements. It is especially useful for angled lifts, doors, hatches and trapdoors where force changes as the mechanism moves.
After calculating, compare the result against product datasheets for force, stroke, retracted length, extended length, speed, duty cycle, voltage and IP rating.
What to Check Before Ordering
- Required force rating
- Required stroke length
- Retracted and extended hole-to-hole length
- Voltage and current draw
- Speed under load
- Duty cycle
- IP rating
- Mounting bracket compatibility
- Control system compatibility
- Feedback requirements
- External limit switch needs
- Clearance through the full motion path
Once your parameters are known, browse electric linear actuators, compare compatible actuator control systems, or contact Progressive Automations for product recommendations. If a standard model does not match your required force, stroke, voltage, or dimensions, review custom linear actuator options.
FAQ About Linear Actuator Force and Stroke Calculations
How do I calculate linear actuator force?
For simple vertical motion, start with the load weight and adjust for actuator angle, friction and safety margin. For hinged motion, calculate torque around the hinge and divide by the actuator’s effective lever arm, then adjust for angle.
Why can an actuator rated above the load still fail to lift it?
The actuator may have poor leverage, a shallow mounting angle, high friction, side loading, binding, insufficient current or too little safety margin. Load weight alone does not determine required actuator force.
Does actuator stroke equal load movement?
Not always. If the actuator moves in the same line as the load, stroke and load movement may be similar. If the actuator is mounted at an angle or moves a hinged object, stroke must be calculated from the change in distance between mounting points.
How much safety margin should I add?
The right margin depends on the application. Add more margin for friction, outdoor exposure, shock, unknown loads, seals, wind, debris, or high duty cycles. Do not oversize without checking speed, current draw, structure, and brackets.
How does mounting angle affect actuator force?
A shallow mounting angle reduces mechanical advantage and increases required actuator force. A steeper angle usually improves lifting efficiency but may require different mounting space or stroke length.
When do I need feedback?
Feedback is useful when you need position control, presets, repeatable stopping points, or synchronized motion between multiple actuators.