How to Calculate the Required Holding Force for a Magnetic Mount

A magnetic mount may appear strong when it is pulled directly from a thick steel test plate. Put the same magnet on a painted vertical surface, add vibration and move the load away from the contact face, and its performance can be very different.

This is why choosing a magnet solely by its advertised pull force is risky. The rated value is useful for comparing products, but it is not necessarily the safe load capacity of the finished installation.

To select a magnetic mount properly, engineers must consider the weight of the component, load direction, steel condition, air gap, friction, vibration and an appropriate safety factor.

This guide from WZ Magnetics Co., Ltd. explains how to estimate the magnetic holding force needed for an industrial mounting application and how to identify conditions that require testing or a customized magnetic assembly.

What Is Magnetic Holding Force?

Magnetic holding force is the force required to separate a magnet or magnetic assembly from a ferromagnetic surface under defined test conditions.

It may also be described as:

• Pull force
• Pull-off force
• Breakaway force
• Detachment force
• Magnetic attraction force

These terms are often used interchangeably, although the exact test method may vary between manufacturers.

For pot magnets and other industrial holding magnets, pull force is commonly measured by placing the magnet against a clean, flat and sufficiently thick steel plate. The magnet is then pulled perpendicular to the surface until it separates.

The maximum measured force is reported in newtons, kilograms-force or pounds-force.

The test value describes performance under that particular setup. It does not account for every condition the magnet may encounter in use.

Pull Force Is Not Load Capacity

Suppose a pot magnet is listed with a pull force of 100 kgf. This does not mean it can safely suspend a 100 kg object in every installation.

The quoted force may have been measured under favorable conditions:

• Direct metal-to-metal contact
• Thick, flat mild steel
• A clean contact surface
• Perpendicular pull
• Room temperature
• No vibration
• No impact
• Evenly applied load

Real mounting surfaces may be painted, thin, rusty or slightly curved. The load may act sideways, and the equipment may vibrate or move.

For these reasons, the safe working load is normally lower than the laboratory pull-force value.

WZ Magnetics Co., Ltd. recommends treating catalog pull force as a comparison and preliminary selection value. The complete magnetic mounting system should be verified under actual operating conditions before final use.

The Three Main Load Directions

Before performing any calculation, determine how the load acts on the magnet. Pull-off, shear and peeling loads behave differently.

Perpendicular Pull-Off Load

A perpendicular load pulls the magnet straight away from the steel surface.

This is the direction in which most holding magnets provide their highest resistance. It is also the usual direction for a standard pull-force test.

Examples include:

• A magnet holding a panel beneath a horizontal steel beam
• A lifting force acting directly away from a steel plate
• A removable component pulled straight from a machine surface

Even in this favorable direction, surface condition and steel thickness still affect the result.

Shear Load

A shear load acts parallel to the steel surface.

For example, a magnetic mount placed on a vertical wall must prevent the attached component from sliding downward. In this situation, the magnet is not necessarily pulled away from the steel. The load is trying to make it slide.

Resistance to sliding depends heavily on friction:

Ffriction=μNF_{\text{friction}}=\mu NFfriction​=μN

Where:

• FfrictionF_{\text{friction}}Ffriction​ is the available friction force
• $\mu$ is the coefficient of friction
• $N$ is the magnetic force pressing the mount against the surface

A smooth metal-faced pot magnet may have strong perpendicular pull force but relatively limited resistance to sliding. A rubber-coated magnetic mount can provide more friction and protect painted surfaces, although the rubber layer introduces a magnetic gap.

Peeling Load

Peeling occurs when one side of a magnet or mounted component lifts before the rest of the contact face.

Once an edge begins to lift, a local air gap forms. Magnetic attraction decreases quickly as this gap grows, making progressive separation easier.

Peeling can occur when:

• The load is applied away from the magnet face.
• A bracket acts as a lever.
• The mounted component is not balanced.
• The contact surface is curved.
• The mounting plate bends under load.

Magnetic mounts should be arranged so the load stays close to the contact surface and is distributed evenly whenever possible.

A Practical Preliminary Calculation

For an initial estimate, the required rated pull force can be calculated using:

Fr=W×SEF_r = \frac{W \times S}{E}Fr​=EW×S​

Where:

• FrF_rFr​ = required rated pull force
• $W$ = actual static load
• $S$ = selected safety factor
• $E$ = estimated application efficiency

Application efficiency represents how much of the catalog pull force may remain after accounting for real working conditions.

For example, if a 20 kg component is mounted under conditions estimated to retain 50% of the rated pull force, and a safety factor of 3 is applied:

Fr=20×30.5=120 kgfF_r = \frac{20 \times 3}{0.5}=120\text{ kgf}Fr​=0.520×3​=120 kgf

The preliminary selection should therefore have a rated pull force of at least 120 kgf.

This formula is useful for screening possible magnets. It is not a substitute for a complete engineering assessment or physical testing.

Example 1: Perpendicular Static Load

An inspection device weighing 12 kg is attached beneath a horizontal steel structure. The mount is pulled perpendicular to the steel surface.

Assume:

• Component weight: 12 kg
• Safety factor: 3
• Estimated application efficiency: 70%

The preliminary required pull force is:

Fr=12×30.7=51.4 kgfF_r = \frac{12 \times 3}{0.7}=51.4\text{ kgf}Fr​=0.712×3​=51.4 kgf

A practical first selection would therefore have a rated pull force above 52 kgf.

Additional capacity may be needed if the steel is painted, the surface is uneven or the device is exposed to movement.

Example 2: Load on a Vertical Steel Wall

A 10 kg camera system is mounted on a vertical painted steel panel.

This is mainly a sliding problem rather than a direct pull-off problem. The following factors become important:

• Friction between the mount and the painted surface
• Paint thickness
• Location of the camera’s center of gravity
• Vibration from nearby equipment
• Whether cables pull on the camera
• Risk of the bracket rotating or peeling away

A metal-faced pot magnet with a 30 kgf pull-force rating cannot be assumed to hold the 10 kg camera safely.

The system may require:

• A rubber-coated magnetic assembly
• Two or more mounting points
• A bracket that places the load closer to the surface
• A secondary safety cable
• Testing on the actual painted panel

In this situation, calculating weight alone is not enough. A prototype should be tested for sliding, rotation and peeling.

Example 3: A Mount Exposed to Vibration

A work light weighing 5 kg is installed on industrial machinery. Although the static load is small, the machine produces continuous vibration and occasional shock.

A magnetic mount selected only for a 5 kg static load may move gradually during operation. Repeated micro-sliding can polish the contact surface, damage the coating and eventually change the mount’s position.

A more reliable solution may involve:

• A higher safety factor
• Multiple magnetic contact points
• A rubber-coated magnet
• A mechanical anti-rotation feature
• A safety tether
• Vibration testing

Dynamic applications should be evaluated according to the highest expected acceleration and shock, not only the object’s stationary weight.

How to Select a Safety Factor

A safety factor provides additional capacity for uncertainty, variation and unexpected loading.

There is no single safety factor that suits every magnetic mount. The correct value depends on application risk and the consistency of the working conditions.

A preliminary reference may be:

These figures are starting points rather than guaranteed design rules.

A larger factor may be necessary when:

• The steel surface varies between installations.
• The surface is painted or corroded.
• The magnet is repeatedly removed and repositioned.
• The load is mounted above people.
• Failure could damage valuable equipment.
• Temperature changes significantly.
• The application involves vehicles or moving machinery.
• The exact load direction cannot be controlled.

A magnetic mount should not be the only protection against falling in a safety-critical overhead installation. Mechanical backup, such as a cable, chain, bolt or locking bracket, should be considered.

Estimating Application Efficiency

Application efficiency is an estimate of how much of the rated pull force remains in actual use.

For an initial comparison, engineers may begin with approximate assumptions such as:

These ranges are intentionally broad. Actual results depend on magnet size, steel properties, coating thickness and magnetic circuit design.

A fixed percentage should not be applied to every magnet. Testing is particularly important when the application is close to the required load limit.

How Steel Thickness Affects Holding Force

The steel surface is part of the magnetic circuit. If it is too thin, it may not carry all the flux produced by the magnet.

When the target steel approaches magnetic saturation, adding a stronger or larger magnet may produce little improvement. The limiting factor is no longer the magnet itself but the steel plate.

Thin steel can also flex under load. Flexing may introduce peeling and reduce the effective contact area.

When requesting a recommendation from WZ Magnetics Co., Ltd., provide the target steel grade and thickness whenever possible. These details are particularly important for:

• Sheet-metal enclosures
• Vehicle body panels
• Storage cabinets
• Temporary steel partitions
• Thin machine covers

Testing a magnet on a thick steel workbench does not accurately represent its performance on a thin sheet-metal panel.

The Effect of Paint and Other Air Gaps

Magnetic force is highly sensitive to the distance between the magnet and the target steel.

Common sources of a gap include:

• Paint
• Powder coating
• Zinc coating
• Rubber
• Plastic film
• Adhesive
• Rust
• Dust
• Surface roughness

The reduction is not determined only by the coating material. Its thickness and uniformity also matter.

A magnet that works well on bare steel may provide noticeably less holding force on a heavily powder-coated panel. Stacking several non-magnetic layers can reduce performance further.

When the finished product attaches to coated steel, it should be tested on the same surface rather than on an uncoated substitute.

Contact Area and Surface Flatness

Catalog pull force normally assumes that the entire magnetic working face contacts the steel.

Actual contact may be reduced by:

• Curved steel
• Raised welds
• Scratches
• Debris
• Uneven coatings
• Deformed sheet metal
• Incorrect installation
• Damage to the magnet face

A small high point can prevent the rest of the magnet from contacting the steel. Although the visible gap may appear insignificant, it can cause a substantial loss of force.

For curved tanks, pipes and steel structures, a flat pot magnet may not be the best choice. A mounting assembly designed to match the surface profile can provide more consistent performance.

Friction and Rubber-Coated Magnets

Friction becomes critical when a magnetic mount is installed on a vertical or inclined surface.

Rubber-coated magnetic assemblies can offer:

• Better resistance to sliding
• Protection for paint and finished surfaces
• Reduced impact during installation
• Improved grip on slightly irregular surfaces
• Additional environmental protection

However, rubber also creates distance between the magnets and the steel. This reduces direct pull force compared with an equivalent metal-faced assembly.

The goal is therefore not simply to maximize catalog pull force. The design must balance:

• Magnetic attraction
• Friction
• Surface protection
• Environmental resistance
• Required dimensions

WZ Magnetics Co., Ltd. can adjust the number, arrangement and grade of the internal magnets to develop a rubber-coated assembly for a specific mounting requirement.

Center of Gravity and Leverage

The position of the load relative to the magnetic surface affects how the assembly behaves.

If a heavy component projects far from the steel surface, it creates a turning moment:

$$M=F\times d$$

Where:

• $M$ is the turning moment
• $F$ is the applied force
• $d$ is the distance from the mounting surface

The greater the distance, the more likely the mount is to rotate or peel away.

This is common with:

• Cameras
• Long brackets
• Antennas
• Work lights
• Sensors on extension arms
• Cable supports

Moving the center of gravity closer to the steel surface can sometimes improve stability more effectively than using a stronger magnet.

Using two magnets spaced apart can also increase resistance to rotation.

Multiple Magnets Do Not Always Add Up Perfectly

It is tempting to assume that two magnets with a rated force of 50 kgf will always provide a combined force of 100 kgf.

That may be approximately true under an ideal and evenly distributed perpendicular load, but real assemblies often behave differently.

Possible reasons include:

• One magnet contacts the steel before the other.
• The mounting plate bends.
• Surface height varies.
• The load is distributed unevenly.
• One magnet starts peeling first.
• Nearby magnetic fields interact.
• Assembly tolerances introduce gaps.

A rigid mounting plate and consistent contact surfaces help distribute the load. The complete multi-magnet assembly should still be tested as a unit.

Temperature and Holding Force

Magnetic output changes with temperature. Neodymium magnets generally lose part of their magnetic strength as temperature rises, although much of this reduction may recover after cooling if the magnet remains within a safe working range.

If the temperature exceeds the limit of the selected grade, irreversible demagnetization may occur.

The temperature rating of a magnetic assembly may also be limited by:

• Adhesive
• Rubber coating
• Plastic parts
• Plating
• Thread-locking compound
• Housing material

Provide both continuous and short-term peak temperatures when discussing an application with the manufacturer.

Selecting the Mounting Structure

Once the required holding force has been estimated, the mounting structure must be selected.

Common options include:

• Countersunk pot magnets
• Pot magnets with internal threads
• Pot magnets with external studs
• Cylindrical bore pot magnets
• Hook magnets
• Eyebolt magnets
• Rubber-coated magnets
• Custom magnetic assemblies

The connection between the magnet and the mounted component should be capable of carrying the intended load. A strong magnet does not compensate for an undersized thread, weak bracket or unsuitable adhesive.

When Physical Testing Is Essential

Calculation helps narrow the options, but testing is essential when the application includes:

• Vertical loading
• Vibration or shock
• Painted or rough steel
• Curved contact surfaces
• High or low temperatures
• Outdoor exposure
• Thin sheet metal
• Long brackets
• Repeated repositioning
• Safety-critical loads

A useful test should reproduce actual conditions, including:

• Target steel material and thickness
• Surface coating
• Load direction
• Bracket geometry
• Temperature
• Vibration
• Installation method
• Expected service time

Short pull tests alone may not reveal gradual sliding, adhesive creep, coating wear or fatigue.

Information WZ Magnetics Needs for an Evaluation

To help WZ Magnetics Co., Ltd. evaluate a magnetic holding application, provide:

1. Weight of the mounted component
2. Load direction
3. Target steel grade and thickness
4. Surface coating and estimated thickness
5. Magnet installation space
6. Working temperature
7. Vibration and shock conditions
8. Indoor or outdoor environment
9. Required mounting structure
10. Position of the load’s center of gravity
11. Required service life
12. Prototype and annual quantities

Drawings, photographs and short application videos can make the evaluation more accurate.

Magnetic Mount Selection Checklist

Before finalizing the design, confirm:

• The pull-force test method is understood.
• Load direction has been identified.
• Steel thickness is sufficient.
• Paint and other gaps have been considered.
• The center of gravity is close to the surface.
• Friction is sufficient for vertical mounting.
• Vibration and impact have been included.
• The correct temperature grade is used.
• The mounting thread or bracket is strong enough.
• A suitable safety factor has been applied.
• A mechanical backup is included where necessary.
• The complete assembly has been tested.

Magnetic holding force calculation starts with the object’s weight, but weight is only one part of the problem.

A reliable design must account for pull direction, friction, steel thickness, air gaps, temperature, vibration and leverage. The catalog pull-force rating can help compare magnets, but it should not be treated as the safe working load of the finished installation.

The most effective approach is to:

1. Identify the real load condition.
2. Estimate the loss caused by the working surface and environment.
3. Apply an appropriate safety factor.
4. Select a suitable magnet and mounting structure.
5. Test the complete assembly under actual conditions.

WZ Magnetics Co., Ltd. designs and manufactures pot magnets, rubber-coated magnets and custom magnetic holding systems for industrial applications. Send us your application drawing, load, steel surface and working conditions for an initial technical evaluation.

Frequently Asked Questions

How is magnetic holding force measured?

It is generally measured by attaching the magnet to a defined steel plate and pulling it perpendicular to the surface until separation occurs. The steel thickness, surface finish, pull speed and test fixture can affect the result.

Is magnet pull force the same as safe working load?

No. Pull force is usually a laboratory test result. Safe working load must account for load direction, surface condition, vibration, temperature and a suitable safety factor.

How do I calculate the required magnet strength?

A preliminary calculation is:

Required pull force=actual load×safety factorestimated application efficiency\text{Required pull force} = \frac{\text{actual load}\times\text{safety factor}} {\text{estimated application efficiency}}Required pull force=estimated application efficiencyactual load×safety factor​

The result should be verified through testing.

Why does a magnet slide on a vertical surface?

Sliding occurs when the downward load exceeds the available friction between the magnet and the steel. A rubber-coated magnet, larger contact area or multiple mounting points may improve resistance to sliding.

Does paint reduce magnetic holding force?

Yes. Paint creates a non-magnetic gap between the magnet and the steel. The effect depends on coating thickness, magnet geometry and magnetic circuit.

Does thicker steel improve magnetic force?

It can improve the result when the original steel is too thin to carry the available magnetic flux. Once sufficient thickness is reached, adding more steel may provide little additional benefit.

Can I add together the pull force of several magnets?

Only as a preliminary estimate. Uneven contact, mounting plate flexibility and load distribution can prevent multiple magnets from sharing the load equally.

What safety factor should be used for a magnetic mount?

The correct factor depends on the application. Controlled static installations may begin with a lower factor, while vertical, vibrating, mobile or overhead applications require a higher factor and more extensive testing.

Should I use a pot magnet or a rubber-coated magnet?

A pot magnet is often preferred when maximum direct pull force is required on clean steel. A rubber-coated magnet may be more suitable for painted surfaces or applications where friction and scratch protection are important.

Can WZ Magnetics design a custom magnetic mount?

Yes. WZ Magnetics Co., Ltd. can develop magnetic assemblies based on the required holding force, dimensions, mounting method, working temperature, target surface and environmental conditions.