SSKC-023 | Simple Signman Knowledge Center

Magnet Working Distance Explained: Why Magnetic Force Drops with Distance

A magnet can feel extremely strong when it is touching steel — but surprisingly weak only a short distance away.

This leads to an important application question:

“How far away will my magnet still work?”

There is no universal working distance for a permanent magnet.

Magnetic performance at a distance depends on the magnet’s size, shape, grade, magnetization direction, pole geometry, target material, magnetic circuit, and the amount and type of separation between the magnet and its target.

Table of Contents

• 1. What Is Magnet Working Distance?
• 2. Working Distance vs Air Gap
• 3. Why Magnetic Force Drops with Distance
• 4. Why Surface Gauss Does Not Tell the Whole Story
• 5. Magnet Size and Working Distance
• 6. Shape, Geometry, and Aspect Ratio
• 7. Does a Higher Grade Increase Working Distance?
• 8. Magnetization Direction and Pole Geometry
• 9. What Is the Magnet Acting On?
• 10. Practical Example
• 11. How to Select a Magnet for a Required Distance
• 12. How to Test Working Distance
• 13. Common Selection Mistakes
• 14. Frequently Asked Questions

1. What Is Magnet Working Distance?

For practical application design, working distance is the separation at which the magnet must perform its intended function.

That function might be:

• holding a steel component;
• attracting through a plastic housing;
• operating a magnetic sensor;
• activating a reed switch;
• coupling two components through a nonmagnetic barrier;
• positioning or detecting an object;
• creating attraction between two magnetic assemblies.

The important question is therefore not simply:

“How strong is the magnet?”

It is:

“What magnetic performance is available at the distance where the application actually operates?”

2. Working Distance vs Air Gap

The terms are closely related, but they are useful for describing slightly different design questions.

An air gap is the separation in the magnetic circuit between the magnet and the target. Paint, adhesive, plastic, rubber, protective films, surface irregularities, and actual air can all contribute to the effective gap.

Working distance describes the distance at which the application needs the magnetic field or force to perform a function.

For a detailed discussion of separation and holding force, see SSKC-012 — The Air Gap Effect.

3. Why Magnetic Force Drops with Distance

A permanent magnet creates a magnetic field around itself.

As the measurement or target position moves farther away from the magnet, the field available at that location generally decreases.

The exact relationship is not represented by one universal formula for all practical magnets.

It depends on factors including:

• magnet geometry;
• dimensions;
• magnetization direction;
• pole arrangement;
• magnetic material and grade;
• target geometry;
• presence of steel components in the magnetic circuit.

This is why a simple rule such as “double the distance and lose a fixed percentage of force” should not be used universally.

4. Why Surface Gauss Does Not Tell the Whole Story

Surface gauss can be useful for characterizing a magnet, but it does not directly tell you how much holding force or field will be available several millimetres away.

Two magnets can have similar surface flux-density measurements while producing different field profiles at a working distance because their:

• diameters differ;
• thicknesses differ;
• shapes differ;
• magnetization directions differ;
• pole geometries differ.

The measurement itself also depends on probe position, distance, orientation, and test method.

For more information, see SSKC-015 — Magnetic Flux Density: Gauss and Tesla Explained.

5. Magnet Size and Working Distance

Magnet dimensions can have a major influence on the shape and reach of the magnetic field.

For example, increasing the dimensions of a magnet may change its field distribution and can improve performance at a specified distance.

This is one reason a physically larger magnet of a lower grade may sometimes outperform a smaller high-grade magnet at the required working position.

However, there is no universal rule that a certain increase in diameter or thickness produces a specific increase in working distance.

The actual geometry should be evaluated for the application.

6. Shape, Geometry, and Aspect Ratio

Discs, blocks, rings, rods, and other magnet shapes produce different field distributions.

Even magnets made from the same material and with similar volume can behave differently because of their geometry.

Important variables include:

• diameter-to-thickness ratio for discs;
• length, width, and thickness for blocks;
• inside and outside diameter for rings;
• pole-face area;
• magnetization direction.

See SSKC-017 — Magnet Shape and Aspect Ratio.

7. Does a Higher Grade Increase Working Distance?

Increasing from a grade such as N35 to N42 or N52 can increase the available magnetic performance when the geometry and operating conditions are appropriate.

But a higher grade does not automatically solve a working-distance problem.

If the application is limited primarily by geometry, target steel, air gap, temperature, or magnetic circuit design, changing grade alone may provide less improvement than expected.

Sometimes changing the magnet's dimensions or magnetic circuit can be more effective than simply selecting a higher grade.

See SSKC-016 — Magnet Size vs Grade.

8. Magnetization Direction and Pole Geometry

Working distance also depends on where the magnetic poles are located.

A disc magnetized axially behaves differently from a similar disc magnetized diametrically.

A multipole magnet can create a strong field pattern close to its surface, but the useful field distribution at greater distances can be very different from that of a simpler pole arrangement.

The correct configuration depends on the application.

For more information, see SSKC-018 — Magnetization Direction Explained.

9. What Is the Magnet Acting On?

Working distance cannot be evaluated without defining the target.

The magnet may be interacting with:

• a steel plate;
• thin sheet metal;
• another permanent magnet;
• a Hall sensor;
• a reed switch;
• a magnetic latch;
• a specialized magnetic assembly.

These are fundamentally different applications.

Magnet-to-Steel

The steel becomes part of the magnetic circuit. Its thickness, geometry, material properties, and available area can affect the resulting force.

See SSKC-011 — How Steel Thickness Affects Magnet Holding Force.

Magnet-to-Magnet

Polarity, alignment, magnetization direction, geometry, and relative position become especially important.

Magnet-to-Sensor

The relevant requirement may be a minimum or maximum magnetic flux density at a specific sensor location rather than mechanical holding force.

10. Practical Example

Suppose a product requires a magnet located behind a 5 mm plastic housing to attract a steel component.

The wrong approach would be to select the magnet only from its direct-contact pull-force rating.

The design should instead evaluate:

The relevant specification is therefore not simply:

“I need a 50 lb magnet.”

A much better requirement is:

“I need the assembly to provide the required functional force at a 5 mm working distance against this defined target under these operating conditions.”

11. How to Select a Magnet for a Required Distance

Step 1: Define the actual working distance.

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Step 2: Define what the magnet must interact with.

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Step 3: Define the required force or magnetic field at that distance.

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Step 4: Define the available magnet dimensions and geometry.

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Step 5: Evaluate grade, magnetization direction, and pole configuration.

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Step 6: Include steel, coatings, housings, and other components in the magnetic circuit.

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Step 7: Evaluate temperature, tolerances, movement, and environmental conditions.

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Step 8: Test the actual or representative assembly at the required distance.

12. How to Test Working Distance

A useful working-distance test should reproduce the actual application as closely as practical.

Document:

• magnet part number and grade;
• magnet dimensions;
• magnetization direction;
• target material and dimensions;
• distance between magnet and target;
• materials within that distance;
• measurement direction;
• temperature;
• test method;
• required pass/fail performance.

For holding applications, measure the relevant mechanical force at the actual working gap.

For sensor applications, measure the relevant magnetic field at the sensor location using an appropriate method and documented probe orientation.

13. Common Selection Mistakes

• Selecting a magnet only from its direct-contact pull-force rating.
• Assuming surface gauss determines working distance.
• Ignoring plastic, glass, adhesive, or other separation.
• Assuming a higher grade automatically solves a distance problem.
• Ignoring magnet dimensions and pole geometry.
• Testing against different steel than the actual application.
• Measuring the field at an undefined distance.
• Ignoring manufacturing tolerances in the final gap.

14. Frequently Asked Questions

How far can a neodymium magnet reach?

There is no single maximum distance. Useful working distance depends on magnet size, geometry, grade, magnetization, target, and the amount of force or field required by the application.

Does a stronger magnet work farther away?

Potentially, but grade is only one variable. A larger or differently shaped magnet may sometimes provide better performance at the required distance than a smaller magnet of a higher grade.

Can a magnet work through plastic?

Yes. Most common nonmagnetic plastics do not block a static magnetic field in the way ferromagnetic steel redirects magnetic flux. However, the plastic creates physical separation, and that additional distance can substantially reduce available force.

Can a magnet work through glass?

Yes, but again the thickness of the glass increases the separation between the magnet and target. The complete assembly should be evaluated at the actual distance.

Does doubling the distance cut the force in half?

Not as a universal rule. The relationship between distance and force depends strongly on magnet geometry, target geometry, and the magnetic circuit.

Should I specify surface gauss or gauss at a working distance?

If the application depends on magnetic field at a particular location, specifying the required field at that location is generally more meaningful than relying only on a surface measurement.

Safety Reminder

Do not assume that a magnet that appears weak at a distance will remain weak as it approaches another magnet or steel component.

Attraction can increase rapidly as the gap closes, potentially creating pinch, impact, or breakage hazards.

Powerful neodymium magnets should be handled with appropriate controls and protective measures.

Working Distance as Part of the Complete Magnetic System

Working distance should be considered together with required holding force, number of magnets, target steel, geometry, load direction, and environmental conditions.

Continue with:

• SSKC-021 — How to Calculate the Magnet Holding Force You Actually Need
• SSKC-022 — How Many Magnets Do You Need?
• SSKC-020 — How to Specify a Custom Magnet

Simple Signman — Canada’s Leading Source for Flexible Magnetic Materials and Neodymium Magnets.

Sharing our magnetic expertise since 1969.