How to Calculate the Pull Force You Need for a Neodymium Magnet
Introduction
One of the most common questions we hear is: “How strong of a magnet do I need?”
Whether you’re designing a magnetic latch, a holding fixture, or a sensor, selecting the right pull force is critical. Too weak, and the magnet won’t hold; too strong, and you may damage components or struggle with assembly.
In this guide, we’ll explain how pull force is measured, how to calculate what you need, and what factors influence real-world holding strength.
What Is Pull Force?
Pull force is the amount of force required to pull a magnet away from a flat, thick steel plate. It’s measured in kilograms (kg) or pounds (lb) . This is the standard rating used by manufacturers to compare magnet strength.
For example, a magnet rated with a 10 kg pull force can theoretically hold 10 kg against a steel surface under ideal conditions.
Important: Pull force is not the same as “how much weight can this magnet lift?” in real applications—because actual holding strength depends on many variables.
Step 1: Determine Your Required Holding Force
Start by asking:
What am I holding? (weight of the object)
How is the magnet mounted? (attached to steel? between two plates? holding against gravity?)
What’s the safety factor? (add 2–4x for safety, especially if there’s vibration or shock)
Basic formula:
Required magnet pull force = (Object weight) × (Safety factor)
Example: You want to hold a 5 kg steel door closed. With a safety factor of 3 (to account for vibration when closing), you’d need a magnet with at least 15 kg of rated pull force.
Step 2: Understand Real-World Reduction Factors
A magnet’s rated pull force assumes:
Perfect contact with a clean, flat, thick steel surface
Pull force applied perpendicularly (straight pull)
No air gap
In reality, these factors reduce holding strength:
| Factor | Reduction |
| Air gap (non-perfect contact) | Even 0.1 mm gap can reduce force by 30–50% |
| Thin steel surface | If steel is thinner than the magnet’s magnetic circuit, force drops |
| Shear force (sideways pull) | Shear strength is about 20–30% of rated pull force |
| Coated or painted surface | Adds a small air gap |
| Vibration or shock | Requires higher safety factor |
Tip: Always choose a magnet with 2–4 times the theoretical required force to account for real-world conditions.
Step 3: Use a Magnet Pull Force Chart
Manufacturers provide pull force ratings for each magnet size and grade. Below is a simplified example for common N42 disc magnets:
| Diameter (mm) | Thickness (mm) | Grade | Rated Pull Force (kg) |
| 10 | 2 | N42 | 1.5 |
| 10 | 5 | N42 | 4.2 |
| 20 | 5 | N42 | 12.0 |
| 20 | 10 | N42 | 25.0 |
| 30 | 10 | N42 | 45.0 |
You can use such charts to quickly find a magnet that meets your pull force requirement.
Step 4: Calculate for Non-Steel Applications
If your magnet is not attaching to steel (e.g., holding two magnets together, or attaching to a non-ferrous material), the pull force is different.
Two magnets attracted to each other: The pull force is approximately the same as one magnet’s rating against steel (because each contributes).
Magnet to thin steel: Force decreases if the steel is thin. Use a factor of 0.5–0.8 depending on thickness.
Magnet to ferritic stainless steel: Lower attraction; may be 30–70% of carbon steel.
Step 5: Consider the Magnet Grade
Higher grade (N52) provides more pull force than lower grade (N35) for the same size.
If you need more holding strength without increasing magnet size, switch to a higher grade.
Example:
A 20×10 mm N35 disc might have a pull force of 20 kg, while the same size N52 could deliver 27 kg.
Step 6: Testing Before Finalizing
When possible, test a sample magnet in your actual application. Theoretical calculations give you a starting point, but nothing beats real-world testing.
We offer custom sampling so you can verify performance before committing to large orders.
Internal Links
N35 vs N42 vs N52: Which Grade to Choose (link to article 1)
Common Neodymium Magnet Applications
How to Protect Neodymium Magnets from Rust
Conclusion
Choosing the right pull force is a balance between theory and real-world conditions.
Determine the weight you need to hold and apply a safety factor (2–4x).
Account for air gaps, surface thickness, and pull direction.
Use a magnet pull force chart to select a candidate magnet.
Test with a sample.
If you need help selecting the perfect magnet for your project, reach out to our team – we’ll recommend the right size, grade, and coating based on your specific application.