Introduction to Electromagnet Holding Force for Your Application
There is one parameter that becomes especially important when choosing the electromagnet for industrial equipment, automation systems, access control, material handling, fixtures, robotics, and other holding applications—electromagnet holding force.
Selection of an electromagnet with insufficient holding force may lead to unexpected releasing of the workpiece, unstable operation, equipment damage, and safety issues. Using an excessively strong electromagnet may affect the size, energy consumption, cooling, and costs of the entire system.
So what amount of electromagnet holding force do you actually need?
It is much more than mere calculation of the object’s weight. Engineers should take into account the magnetic contact area, air gap, target material, target thickness, surface condition, temperature, load direction, vibration, acceleration, supply voltage, duty cycle, and an appropriate safety factor.
In this guide, we describe how to calculate the holding force of an electromagnet, what factors may affect the available force, and how to select a proper holding electromagnet for your application.
1. What is Electromagnetic Holding Power?
Electromagnet holding force is the magnetic attracting force developed between the electromagnet with applied current and the ferromagnetic target, which is normally a steel armature, steel plate, machine element, or workpiece.
The holding force is normally measured in:
Newton (N)
Kilogram-force (kgf)
Pounds-force (lbf)
Approximate conversion between Newtons and kilograms is shown below:
1 kgf = 9.81 N approx.
Thus, for example, an electromagnet with a rated holding force of 500 N theoretically produces the following force:
~ 51 kgf (500/9.81)
But it doesn’t mean that you should use an electromagnet of 500 N to lift and safely hold a 51 kg object.
Rated values are normally determined under certain test conditions in the laboratory, and it might include:
Clean and flat steel target
Full magnetic contact with the armature
Certain target thickness
Rated voltage
Minimum air gap or none.
Practical applications usually have completely unique conditions.
Your application may involve:
Paint, rust, dust, oil
Vibration
Acceleration
High temperature
Thin steel
Curved surface
Mechanical misalignment.
All of those can negatively impact the available magnetic holding fotofore, in order to select reliable electromagnets, the force should be calculated with the necessary safety factors and derating.
2. The Basic Formula of Electromagnet Holding Force
For an ideal magnetic circuit with a uniform magnetic field and a very small air gap, the theoretical electromagnet holding force can be calculated as
F = B^2 * A / 2 * μ₀
Where:
F = holding force of electromagnet, N
B = magnetic flux density, T
A = magnetic pole area, m²
μ₀ = permeability of free space (approx. 1.2566 × 10⁻⁶ H/m)
Thus, the electromagnet holding force equation demonstrates that the following parameters strongly affect magnetic force:
Magnetic flux density (B)
Pole area, efficiency
It is possible to increase the available electromagnet holding force by increasing the pole area, provided that the magnetic circuit is capable of sustaining the required amount of magnetic flux.
But the relation to the magnetic flux density is even more important, as the electromagnet holding force is proportional to B2.
In an ideal magnetic circuit, if you double the density of the magnetic flux, you quadruple the holding force.
But real electromagnets have some drawbacks.
The actual force that can be developed is affected by magnetic saturation, flux leakage, air gaps, coil heating, target material properties, and electrical limitations.
Therefore, theoretical equations are useful for engineering estimates, but testing and application-specific measurements should be made for the selection of the final product.
2.1 Example of Electromagnet Holding Force Calculation
Let’s assume an ideal electromagnet with the following parameters:
Magnetic flux density (B) – 0.8 Tesla
Pole area (A) – 400 mm²
First, let’s convert the area of the pole to square meters:
400 mm² = 0.0004 m²
Now we can apply the holding force equation:
F = \frac{1}{2\mu_0} A B^2
Substituting the values:
F = (0.8^2 * 0.0004) / (2 * 1.2566 * 10^-6)
Theoretical holding force is approximately equal to:
F = 102 N
Let’s convert this value to kgf:
102 ÷ 9.81 = 10.4 kgf (approx.)
Thus, the theoretical electromagnet holding force under ideal conditions equals:
10.4 kgf or 102 N
But this is a theoretical value only.
Let’s suppose that your real-world application is such that the electromagnet is able to produce only 60% of the ideal force due to surface conditions, a small air gap, temperature, or poor contact.
Then the force that can be used is
102 × 0.60 ≈ 61 N
This example shows that an electromagnet chosen on the basis of the theoretical estimate only could be an undersized product.
3. How Much Electromagnetic Holding Force Do You Need? A Step-By-Step Guide
In many cases, the easiest approach is to calculate the load force.
For a hanging object:
Fload = m g
Where:
m = mass (kg)
g = gravitational acceleration (about 9.81 m/sec²)
Let’s say your application requires holding an 8 kg steel part.
The gravitational force is
8 x 9.81 = 78.5 N
That means that the electromagnet has to generate a useful holding force of more than 78.5 N in order to counter the static load.
But selection of the electromagnet with 78.5 N of force will leave almost no safety margin.
Step 1: Find the Fundamental Load Force
8 kg x 9.81 = 78.5 N
Step 2: Add a Safety Factor
Let’s suppose that your engineering estimate shows that the safety factor of 2.5 is required.
Thus, the necessary usable holding force is
78.5 x 2.5 = 196.25 N
Your application requires approximately:
196 N usable gripping force
Step 3: Take into Account Derating
If the surface condition, temperature, air gap, and other factors make it possible to use only 60% of the nominal rated force.
Nominal force that has to be supplied from the electromagnet:
196.25/0.60 ≈ 327 N
In this case, you need to select an electromagnet with the minimum nominal electromagnet holding force of approximately 327 N.
It is completely different from a statement like “Let’s use a 100 N electromagnet because the real object weighs only 8 kg.”
The selection of the final product should always be validated in the real operating conditions.
4. Factors that Affect the Electromagnet Holding Force
The nominal electromagnet holding force indicated in the electromagnet catalog is not necessarily the exact force that will be generated inside your machine.
Understanding of those factors can help you to select the correct electromagnet and prevent performance problems.
4.1 Air gap
Air gap is the main factor that affects the electromagnet holding force.
Normally, the maximum electromagnet holding force is reached when the electromagnet pole face is in direct full contact with the steel target.
Even a small gap between the surfaces increases magnetic reluctance and reduces the magnetic attraction.
Factors that can create an effective air gap can include:
Paint, Dust, Dirt, Rust, Oil, Glue
Plastic films
Surface coatings
Uneven surfaces
Curved workpieces
Mechanical misalignment.
Even a very small non-magnetic air gap greatly reduces the magnetic force.
Do not rely only on the maximum zero-gap holding-force specification. if your application requires an electromagnet holding force to attract the target from a distance.
Instead, refer to the manufacturer’s force versus air gap graph.
4.2 Target Material
An electromagnet has to have a certain ferromagnetic target.
Low carbon steel is normally used due to its magnetic properties.
But different materials can have very different results.
For example, not all stainless steels are strongly attracted by an electromagnet. Some grades of stainless steel are slightly attractive, and others are practically unsuitable for the holding application.
If you are not sure about the suitability of your workpiece, please indicate the exact material grade when you request advice on the electromagnet.
Then the manufacturer can estimate the magnetic circuit more precisely.
4.3 Target Thickness
Steel target thickness also may affect the electromagnet holding force.
If the target plate is too thin, it cannot effectively conduct the required magnetic flux.
This can reduce the available force due to magnetic saturation.
Thus, if you have a very thin steel plate and the strong electromagnet against it, it may not have the nominal rated holding force.
Always check the manufacturer’s recommendations for armature or target thickness if available.
For the critical applications, it is advisable to test the electromagnet on the real target material and thickness.
4.4 Contact Area and Surface Flatness
For the maximum magnetic electromagnet holding force, the electromagnet pole face has to be in full even contact with the target.
The contact area of the magnetic circuit can be reduced by the warped plate, rough surface, curved component, or improper mounting of the electromagnet.
This may also create more air gaps.
If your application includes irregular shapes, please discuss the geometry with the electromagnet manufacturer at the design stage.
Sometimes a special pole face or special design of electromagnet can perform better than a standard flat holding magnet.
4.5 Coil Voltage and Current
The magnetic field generated by an electromagnet depends on the coil design and electrical current.
In the simplified magnetic circuit, where the air gap is the dominating parameter, magnetic flux density can be approximated as
B ≈ μ₀NI/g Where: N = number of turns of coil
I = current in coil
g = air gap
An increase of the current increases the magnetic flux and holding force up to magnetic saturation and thermal limitation.
But overvoltaging the electromagnet above the nominal rating is not a good way to get additional holding force.
Overvoltage and overcurrent may cause overheating of the coil, degradation of insulation, reduction of service life, or failure of the electromagnet.
Always operate the electromagnet within the following parameters:
4.6 Operating Temperature
Operating temperature may have a significant impact on electromagnet holding force performance.
As the copper coil heats up, its electrical resistance rises.
When a constant voltage power supply is used, the coil current decreases when the resistance rises.
As a result, the magnetic field may reduce as well.
As a consequence, the behavior of the electromagnet in the hot state can be significantly different from that in the original cold state.
Especially in cases when the operation needs:
Continuous operation
High duty cycle
High environmental temperature
Restrictions in ventilation
Enclosed device
When selecting electromagnets, please pay attention to whether the holding-force specification takes into account:
Cold state of coil
Consistent operating temperature
Rated voltage
Defined duty cycle
4.7 Vibration, shock, and direction of load
The electromagnet holding force specifications generally refer to the magnetic attraction in the direction perpendicular to the contact surface.
In real-life applications, however, the force can be applied parallel to the surface.
In such cases, the application may depend highly on friction.
The simplified formula would be as follows:
Ffriction = μ * Fnormal
Where:
μ – friction coefficient
Normal—normal magnetic force
Friction can depend on oil, moisture, surface finish, contamination, and wear.
Thus, an electromagnet holding force that can generate sufficient direct pull force may fail to resist the same load when it is applied sideways.
If you are planning to use large side loads, vibration, acceleration, or shocks in your application, the following mechanical features may be considered:
Physical stops
Guide rails
Hook pins
Feature location
Supports for safety
Do not rely on electromagnets to carry all mechanical loads by themselves at all times.
5. Pull-In Force vs. Holding Force
It is quite an essential difference when selecting an electromagnet.
Usually, holding force is a magnetic force when the electromagnet and target are already in close contact.
While pull-in force is a magnetic attraction that can be produced in case there is an air gap between the electromagnet and the target.
The bigger the air gap, the lesser the magnetic force. This means that an electromagnet that has a high holding force rating at contact may have significantly lower pulling force just several millimeters away.
In case your machine needs an electromagnet to pull a steel part with an initial gap of 3 mm, the maximum holding-force rating at zero gap will not be enough for the product selection.
You should be aware of:
Baseline air gap?
Power contained in that gap?
Force change during movement?
Is there enough force to counterbalance the load?
That’s when holding force versus gap data provided by the manufacturer can help.
6. How to Select the Right Holding Electromagnet
When buying electromagnets, do not focus only on the electromanget holding force of a product.
The selection process should include the entire application.
Make sure you have the following information before contacting an electromagnet manufacturer:
Hold Force Required [N or kgf]
Weight of load
Direction of load
Target material
Target thickness
Available Contact Area
Initial gap air gap
Final air gap:
Power supply voltage
Now out now available
Duty cycle continuous/intermittent
Temperature of surroundings
Maximum working temperature
Available installation sizes
Response Time Required
Release time needed
Shock and vibration conditions
Environmental requirements
By providing this information, the manufacturer will be able to suggest an electromagnet that is suitable for the real-world application, rather than just matching one catalog force spec.
7. Electromagnet: Off-the-Shelf vs. Custom
Common electromagnets can be suitable for various industrial applications due to the benefits they offer: availability, shorter development time, and cheaper price.
However, some projects can be hard to solve using a standard product.
In case the application has special requirements concerning it, it may be necessary to design a custom electromagnet.
Holding sway
General dimensions
Mounting arrangement
Voltage.
Power consumption
Duty cycle
Lead wire arrangement
Connector type
Pole geometry
Working temperature
Water-resistant protection
Corrosion resistance;
Special environment requirements
Weilong Intelligent Technology (Dongguan) Co., Ltd. specializes in electromagnet and solenoid solutions and can advise on standard and custom designs depending on the application requirements.
8. The importance of the manufacturer Electromagnet holding force data
Theoretical formulas can be quite helpful in understanding electromagnet behavior, but, where possible, the actual product selection should be based on validated data.
The manufacturer of the electromagnet holding force rating may be checked under the following conditions:
Specific target material
Some thickness of targets
Clean surface conditions
The contact zone is fully closed.
Rating, supply voltage
Coil temperature specification
Defined airgap conditions
If your actual application is different, your actual electromagnet holding force will differ from these test conditions.
In case of a difficult application, it is highly recommended to test the electromagnet with the real workpiece.
This is especially true for cases when your system involves:
Thin steel,
Surface coating
Curved parts
Vibrations
High temperatures
Dynamic loading
Large starting air gaps
9. Need help calculating the strength of an electromagnet’s pull?
The selection of an electromagnet holding force should not be a guess.
Firstly, you should calculate the required load force, then apply an appropriate safety factor, then estimate the actual contact conditions and take into account expected losses, and select the nominal electromagnet rating.
At Weilong Intelligent Technology (Dongguan) Co., Ltd., we can help our customers to estimate electromagnet requirements in accordance with actual application context.
To evaluate an electromagnet for your project, we ask you to provide the following information:
Available installation space + target thickness + target material + load weight + voltage + duty cycle + air gap
Based on the correct application information, electromagnets can be compared more accurately, reducing the risks of undersized or oversized product selection.
10. FAQ: What is the strength of an electromagnet?
10.1 What electromagnet holding force do I need to hold?
First, calculate the load force with:
F = m g
Then multiply by an appropriate safety factor and consider air gaps, surface conditions, target material, temperature, vibration, and load direction.
10.2 How does the airgap influence the electrodynamic holding force?
The magnetic force will be significantly decreased by the increased air gap since the air increases the magnetic reluctance. Paint, rust, dirt, coatings, and rough surfaces can all serve as an effective air gap.
10.3 What is the difference between electromagnet holding force and pull force?
Generally speaking, the electromagnet holding force is measured with the electromagnet and target in close contact. The maximum force available when there is still an air gap is called pull-in force.
10.4 Can I increase the electromagnet holding force by increasing the voltage?
Increasing voltage can increase current and magnetic field strength under certain conditions. An electromagnet should only be operated according to its specified electrical and thermal limitations.
10.5 Why does my electromagnet not develop its rated holding force?
The causes can be air gaps, rough surfaces, coatings, wrong target material, insufficient target thickness, poor alignment, low supply voltage, high temperature, and partial contact.
10.6 Thickness of the steel affects the holding force of an electromagnet?
Yes. In case the steel to be targeted is too thin, magnetic saturation can limit the usable magnetic flux and thus holding force.
10.7 Is the holding force of an electromagnet its safe lifting capacity?
No, not directly. The rated holding force is not necessarily equal to the safe lifting capacity. When developing lifting applications, acceleration, vibration, surface conditions, power loss, safety factors, and applicable safety requirements have to be taken into account.
10.8 What information do you need to order an electromagnet?
Specify desired holding force or load weight, target material and thickness, air gap, supply voltage, duty cycle, operating temperature, available mounting space, load direction, and environmental requirements.
Based on the correct application information, the electromagnet manufacturer will be able to recommend a suitable holding-force range and product configuration.
11. Final thoughts
When selecting an electromagnet for industrial holding, automation, material handling, access control, fixtures, and other applications, it is important to calculate its holding force.
The electromagnet holding force can be calculated theoretically as
F = B²A / (2μ₀)
But theoretical calculation is just the beginning.
The electromagnet holding force depends on the following factors in practical application: air gaps, contact area, surface finish, target material, target thickness, coil temperature, supply conditions, magnetic saturation, load direction, and vibrations.
To be able to select the product successfully, you should calculate the load force, apply a safety factor, take into account expected derating, and then compare this to the manufacturer’s performance data.
But most importantly, do not assume that the maximum catalog electromagnet holding force will be available in your application automatically. The best way to confirm the performance is to conduct tests under actual operating conditions for critical or demanding applications.
Need help selecting an electromagnet holding force for your application?
Please send us the required holding force, voltage, target material, air gap, duty cycle, and available installation dimensions to Weilong Intelligent Technology (Dongguan) Co., Ltd. ([email protected]). We can assist you in choosing the electromagnet configuration that is right for your project.
