Testing Magnet Strength

1. How do you test magnet strength?

Magnet strength can be tested with various methods, but the main method of testing is using a pull force gauge attached to a magnet, placing the magnet directly onto a large block of steel, and measuring the force required to pull the magnet straight away from the steel. Before we go into detail on how each of the 4 pull forces are calculated, we must first talk about the ideal testing situations to get the most accurate results.

Ideal testing conditions for finding a magnet's max strength

• A thick steel plate - Using a thick steel plate with no coating is a must for testing. If the steel reaches maximum saturation of magnetic flux, then there is flux not absorbed by the steel, and the magnet cannot reach it's maximum pull force. The magnetic flux is also 3D in nature and magnetic field lines extend out in all directions. The steel plate must also be at least around double the diameter or width of the magnet in order to absorb the majority of magnetic flux and achieve max pull potential. Steel large enough to fully absorb all magnetic flux is the ideal testing situation.

• Highly magnetic steel - Ensure that the steel used is highly magnetic, as some steels are less than others. This is due to differing amounts of iron content. Less iron included in the alloy creates gaps between iron particles. These gaps may be very small, but they add up when non-magnetic carbons and other molecules are added to the alloy. A low-carbon steel closest to pure iron will be the best for benchmarking. Learn more about magnetic types of steel in our Is Stainless Steel Magnetic? article and calculate ideal steel thickness with our steel thickness calculator.

• Zero gap - Any gap between the magnet and the steel plate will cause a loss in pull force. This can be coating on the steel, an air gap, the magnet not being flush and other paint or coatings. The magnets are technically coated in a thin 15-21 µm thickness plating of nickel, which does slightly decrease max pull force, but not enough to make a major impact. So as close to a zero gap as possible is the ideal testing situation. Check out our magnet gap calculator if you need to calculate magnet pull strength over a distance and our article Measure Magnet Field Strength in a Gap for more info.

• No outside influence - This should go without saying, but clean surfaces, free of debris and sticky residue, with no magnetic fields nearby, ensures that we can test with as few variables as possible in order to get the most accurate results.

Why do you calculate a magnet's maximum strength and not for a specific situation?

If we measured our magnets based on specific conditions, then we would never know their full potential. Thus, by measuring the strongest pull force, we can use basic rules of thumb to estimate a fairly accurate pull force with almost any variable and in almost any condition! In other words, if you have all of the data first, it is easier to subtract than to later try and add the data or retest. Knowing the strongest state of the magnet allows us to subtract pull force based on different variables and principles without redundant testing.

The second reason for measuring the magnet's full potential is that if you test based on common use cases, such as attaching a magnet to a refrigerator door, hanging on a filing cabinet, etc., you end up testing the maximum saturation ability of the steel rather than the magnet. In other words, once the steel is saturated to the max, let's say with a 1" magnet, then even a 4" magnet would have a similar pull force. Using a large, thick steel plate helps achieve the highest force for any magnet size. You can use our steel flux absorption calculator to estimate how much magnetic flux steel will absorb based on thickness.

Our commitment to quality

All tests done here at K&J Magnetics are done with precision equipment specially tailored for measuring the physical and magnetic properties of magnets. We regularly perform calibration tests to make sure equipment readings are accurate and perform incoming material inspections to ensure the quality of our products meet or exceed industry standards. Learn more about K&J Magnetic's quality control process for magnets.

2. How strongly do magnets attract to steel? - Pull Force Case 1

Magnet attraction to steel is based mainly on the size of the steel and ability to absorb the magnet's flux, but there are many factors involved. Here we will review the K&J pull force case 1 in detail. Pull force case 1 is how strong a magnet will be when attracting to a large piece of steel.

Purpose of Pull Force Case 1

Magnet pull force case 1 is to test the maximum strength of a magnet when attaching to a large, flat, plain piece of steel. This provides a benchmark that can be used as a reference when estimating magnet attraction to steel in any situation. This is useful for attaching a magnet to a washer, cup, blank, metal wall or any other metal surface.

Pull Force Case 1 Procedure

1. Check to make sure steel is large enough for magnet.

2. Attach magnet to force gauge securely. Magnets are attached to a screw then inserted into the gauge. For hook style magnets, we use a hook attachment for the gauge.

3. Make sure magnet is centered to eliminate center of gravity/leverage issues and level to prevent gap issues.

4. Pull magnet slowly with force gauge until it separates from the steel base.

5. Record highest (peak) value.

6. Perform several tests and take average of all as final pull force case 1 value. The gauge is connected to a PC, which records force over distance values.

7. Average values and create a magnet strength graph. This graph is available for most magnets on the technical tab and displays the diminishing returns of pull force based on gap or distance.

3. How Strong are Magnets between Steel?

The strength of magnets between steel depends on steel size/thickness and the size and shape of magnet itself. The K&J pull force case 2 measures how strong a magnet will be when placed between two pieces of steel.

Purpose of Pull Force Case 2

The purpose of magnet pull force case 2 is to measure the maximum pull force a magnet can exert when sandwiched between steel in an ideal situation. This measurement can be useful for lifting applications or when strong magnets are needed to hold 2 pieces of metal together tightly.

Pull Force Case 2 Procedure

1. Check to make sure steel on both sides of magnet is large enough for magnet.

2. Attach magnet to upper piece of steel and lower piece of steel.

3. Ensure magnet is flush with both surfaces and upper steel is level with lower steel to prevent leverage issues.

4. Pull with force gauge until magnet separates from either piece of steel.

5. Record highest (peak) value.

6. Take average of multiple test and the average is the pull force case 2 final value. The gauge is connected to a PC, which records force over distance values.

7. Takes all values and plot a magnet strength curve graph. Pull force case 2 strength curve is available for most magnets on the technical tab and displays the diminishing returns of pull force based on gap or distance.

4. How Strong Do Magnets Attract to Each Other?

The strength of two magnets attracting to each other depends on the size of the magnets, but two identical magnets attracting to each other can provide the strongest attraction force possible in many situations. However, it seems counter-intuitive, but two identical magnets directly attracting to each other is equal to a single magnet directly attracting to a large, thick steel plate. The difference comes when the steel is small, thin, or when there is a gap. Two magnets will also self-align, whereas magnets and steel do not self-align. Because there are so many variables when a magnet is attracting to steel, a magnet-to-magnet connection is ideal in many situations.

Purpose of Pull Force Case 3

The purpose of magnet pull force case 3 is to measure the maximum pull force two identical magnets have in an ideal situation. Pull force case 3 is very useful for applications where the same magnet is used on both sides such as box closures, model and miniatures, product parts and other uses where a second magnet is chosen over a steel blank.

Pull Force Case 3 Procedure

1. Attach upper magnet to pull force gauge securely and lower magnet to steel plate.

2. Ensure both magnets are flush with both surfaces to prevent leverage issues and gaps.

3. Pull with force gauge until magnets separate from each other.

4. Record the highest (peak) value before magnets came apart.

5. Average multiple tests to get final pull force case 3 value. The gauge is connected to a PC, which records force over distance values.

6. Plot all values in a graph. Pull force case 3 strength curve is available for most magnets on the technical tab and displays the diminishing returns of pull force based on gap or distance.

5. How Strong Do Magnets Repel Each Other?

Two magnets repelling has almost identical strength as two attracting magnets. The reason there is a difference is that when magnets attract, all field line align and snap into place in a tight space. However, when magnets repel, the field lines are forcefully pushed out to the sides, uncompressing them and causing them to have to travel through air and thus weakening the force. In theory, the further away repelling magnets are, the lesser the impact of the field line spread, but the gap between the magnets has a greater effect and thus would be harder to measure.

Since stability of repelling magnets is extremely difficult to control, we combined physical testing, mathematical calculations and FEMM simulations in combination to provide pull force case 4 values.

Purpose of Pull Force Case 4

The purpose of magnet pull force case 4 is to measure the maximum repulsion force two identical magnets have in an ideal situation. This is useful for levitation and applications like production or assembly lines that may use repelling magnets.

Pull Force Case 4 Procedure

To learn more about how we performed testing for pull force case 4, you can read full detail in our article Repelling Magnet Forces which goes into detail about all testing and calculations we performed.

6. Additional Resources for Understanding Magnet Strength

We talked all about how to measure a magnet's strength using different equipment and tools, but there is too much information to fit into a single article. Below we break down a few additional articles you can review to gain more info on how magnet strength works and how to find out how strong your magnet will be in your specific application or product.

Learn more about magnets' interaction with steel

Some magnet applications may involve another attracting magnet, but many magnets attract to stainless steel. Thus, it is very important to understand the interaction between a magnet and steel. Below is a collection of articles explaining in detail how magnets attract to stainless steel and additional properties.

• Magnets vs. Steel - A guide to how magnet strength is affected by steel.

• Why is Some Stainless Steel Magnetic and Other Stainless Steel is Not Magnetic? - A guide to the types of stainless steel are magnetic and which types that are non-magnetic.

• How Steel Affects Magnet Strength - A guide to stainless steel and how it can extend magnet strength or act as a shield.

• Calculating Steel Thickness for Neodymium Magnets - A guide to finding the right thickness of steel to maximize magnet strength.

• Shielding Magnets - A guide to what materials can be used to shield electronics or other things from a magnetic field.

Other factors that affect a magnet's strength

Below is another list of articles that are a summary of things that can affect how much pull force a magnet will have in a certain situation. Like we said above, tests are done in optimal conditions to find the max strength, then you can subtract more easily later based on other variables.

• Leverage & Friction - A guide to how leverage and friction can decrease a magnet's strength.

• How Strong is a Magnet? - A guide to finding out how strong a magnet is in a certain situation and ways to increase its strength.

• Magnet Strength Grades & Heat Grades - A guide to how strong magnets are per grade and per operating temperature.