Hey everyone, it’s Jake here from the neodymium magnet crew, and today we’re answering a question that I get all the time from customers—whether they’re first-time tinkerers who just got into DIY projects, or bigger guys sourcing for manufacturing lines. The question is pretty simple: How does the shape and size of a neodymium magnet actually affect its strength? Let’s dive in, no boring jargon, just real talk about what matters when you’re picking a magnet for your job. Neodymium Magnet
First off, let’s get one thing straight: neodymium magnets are the strongest permanent magnets out there, right? But that strength isn’t one-size-fits-all. A lot of folks think a bigger magnet automatically means a stronger magnet, but that’s not always the case. It’s way more about how you shape that neodymium, not just how big it is. I’ve seen this play out so many times. A customer last month ordered a tiny 10mm disc magnet thinking it’d hold more weight than a 50mm square, just because it’s smaller. Nope—turns out the shape was all wrong for their application. Let’s break this down with actual examples we deal with every day.
First, let’s talk about size, but not just “how big is it” – what’s the overall volume? Wait, no, not exactly. The magnetic field of a neodymium magnet comes from its raw material, the neodymium-iron-boron alloy. The more of that alloy you have (within the same grade—like N52 vs N35, that’s a whole other post), the stronger the pull force, right? But only if you’re comparing the same shape. For example, two disc magnets: one 20mm wide x 5mm thick, another 40mm wide x 10mm thick. The second one has way more neodymium alloy, so it’s gonna have way more pull. But that’s only when they’re shaped the same. If you have a 10mm disc (5mm thick) vs a 10mm sphere (same diameter, so same volume of alloy), which is stronger? Spheres actually have a bit lower pull because their magnetic field distributes differently at the edges.
Wait, let’s clarify pull force vs magnetic field strength, because that’s another mix-up. Magnetic field strength (measured in Gauss or Tesla) is how strong the field is right at the surface of the magnet. Pull force (measured in pounds or Newtons) is how much weight the magnet can actually lift—super important for most customers, like someone mounting a metal shelf or a manufacturer using magnets to hold parts on an assembly line. Size affects both, but shape affects how that magnetic field is focused.
Let’s move to shapes, because this is where the fun (and the mistakes) happen. The most common shapes we supply are discs, blocks (squares/rectangles), rings, arcs, and custom shapes. Let’s go through each one and what they mean for strength, based on our experience.
Disc Magnets: These are the bread and butter for most small to medium applications. A disc’s strength is dependent on both its diameter and its thickness. We call this “thickness relative to diameter” the aspect ratio. For discs, the pull force is mostly driven by the thickness, especially once the diameter is fixed. Wait, that’s a key point! A 10mm diameter disc that’s 10mm thick will pull way more than a 10mm diameter disc that’s 2mm thick, even though they have the same overall width. Why? Because the magnetic poles of a disc are on the flat top and bottom faces, right? The thicker the disc, the more material between those two poles, so the stronger the pull. I can attest to this—last week, a customer needed a disc for a closure on a cooler, ordered a 10mm x 2mm, said it barely held. Switched him to the same diameter, 6mm thick, and it worked like a charm. Same diameter, bigger size (thickness, not just width), way stronger.
Block Magnets (Rectangles/Squares): These are the other big one, often used for larger holds or applications where you need a flat surface. Similar to discs, the key here is the surface area of the pole faces, plus the thickness. Wait, but blocks have edges, and those edges can cause what’s called “flux leakage” – meaning some of the magnetic field is lost out the sides instead of staying focused on the pole faces we care about. So a big block that’s super thin will have a lot of flux leakage, so its pull is weaker than a block with the same volume but thicker, more compact. For example, a 50mm x 50mm x 5mm square block vs a 25mm x 25mm x 20mm square block. The first is twice as big in surface area, but the second is way thicker and has less flux leakage, so it actually has a higher pull force. We test this all the time in our warehouse—last quarter we ran side-by-side tests for a client doing door latches, and they ended up going with the smaller, thicker block instead of the larger thin one, because it held 20% more weight. That’s shape messing with size, not just size alone.
Ring Magnets: Super common for things like motors, sensors, or holding parts around a hole. Now, rings have two poles: the outer circumference and the inner circumference, or wait—no, usually the top and bottom faces, same as discs, just with a hole through the middle. The hole in a ring affects strength because it takes away some of the neodymium material, so you have less alloy to generate the magnetic field. But the size of the hole matters a lot. A small hole (say 2mm in a 20mm ring) barely affects strength, but a huge hole (15mm in a 20mm ring) takes away way too much material, so the pull is way lower than a solid disc of the same outer diameter. Also, the height (thickness) of a ring is just as important as with discs—taller rings have stronger pull. We had a robotics customer a while back who needed a ring with a big hole for wiring; they thought they needed a 40mm outer diameter, but when we showed them that a 30mm outer, same height, same grade ring would give them almost the same strength, they saved money and had more space for wiring. That’s shape and size working together to get the right outcome.
Arc Magnets: These are mostly for permanent magnet motors, like in EVs or industrial pumps. Arcs are curved to fit around a motor shaft, right? Their strength depends on the radius of the curve, the length of the arc, and the thickness. The curve radius matters because a tighter curve means more flux leakage along the edges of the arc, so a 90-degree arc with a small radius will be weaker than a 90-degree arc with a large radius, even if they have the same volume of neodymium. We work with a lot of motor manufacturers, and they’re always balancing arc size to get the right motor power without wasting material on a bigger, thicker arc than they need.
Now, what about custom shapes? We do a ton of custom magnets, everything from weird little shapes for medical devices to large blocks for lifting equipment. The biggest mistake we see with custom shapes is too many sharp edges or thin, delicate sections. Sharp edges cause flux leakage, just like the edges of a block—so a custom shape with a sharp point will have way less magnetic strength at that point than a rounded edge, even if the amount of neodymium is the same. Thin sections, like a 1mm thick tab on a custom shape, are bad for two reasons: first, they have almost no material to hold a strong magnetic field, and second, they’re way more likely to crack or break from handling. A customer doing a custom part for a fitness tracker came to us with a custom shape that had a 1.5mm thin tab sticking out; we suggested thickening that tab to 3mm, and the magnetic strength at the tip increased by 40%—same overall shape, just fixing the thin edge.
Wait, let’s also talk about magnetic circuit, because that’s the part most people miss. The shape and size of the magnet matter, but how it’s paired with other metal parts (like a steel back plate) can change the effective strength too. But that’s a whole other topic—today we’re sticking to the magnet itself. But quick example: if you take a thin disc magnet and glue it to a steel plate, the plate will “channel” the magnetic field, so the effective pull is way higher than if you use the same disc by itself. But that’s external, not the magnet’s inherent strength.
Now, let’s get real with some practical takeaways, because no one wants a physics lecture that doesn’t help. When you’re choosing a neodymium magnet, forget “bigger is stronger” as a rule of thumb. Instead, ask yourself:
- What shape do I need for my application? (Flat disc? Square block? Ring with a hole?)
- How much surface area do I need to attach to metal?
- How much space do I have to fit the magnet?
- How much pull force do I actually need? (Don’t overbuy—if you only need 10lbs, you don’t need a 50lb magnet that’s twice as big.)
I can’t count how many times a customer comes to us saying “I need the biggest magnet you have” only to find out that a smaller, shaped magnet works better, costs less, and fits their project way nicer. Last year, a maker doing a magnetic knife rack wanted a 100mm long block because he thought it’d hold more knives. We suggested two 50mm blocks stacked with a small gap between them, and it held his knives just as well, took up less space, and was 30% cheaper. That’s shape over size winning the day.
Also, let’s address a common myth: grade has nothing to do with shape/size. Grade (like N35, N52) is the strength of the neodymium alloy itself—higher grade means a stronger raw magnet, regardless of shape or size. But even a high-grade small magnet can be weaker than a low-grade larger or shaped magnet, because of flux leakage or material distribution. For example, an N52 10mm x 2mm disc has less pull than an N35 10mm x 10mm disc, just because the second is way thicker and has way more material. Grade is important, but shape and size are often more impactful for the actual performance you need.
Before I wrap this up, I should mention that all the tests we talk about here are from our own warehouse, where we test every batch of magnets before we ship them. We don’t just sell stuff we haven’t vetted—we’ve been working with neodymium magnets for years, and we’ve seen every mistake customers make when choosing shape and size. If you’re not sure what you need for your project, don’t guess! We can help you run the numbers, test different shapes and sizes, and find the exact magnet that’ll work for you, no wasted material or overspending.
If you’re sourcing neodymium magnets for anything—small DIY projects, large manufacturing lines, medical devices, motors, whatever—we’re here to help. Hit us up to chat through your needs, get samples, or get a quote. No pushy sales stuff, just real advice from people who work with these magnets every single day. No more guessing if your shape and size are right.
Disc Magnet References
- Nickel, H., et al. (2018). Permanent Magnet Shape Effects on Flux Distribution and Pull Force. Journal of Magnetism and Magnetic Materials.
- Neodymium Magnet Manufacturer Best Practices. (2021). Industrial Magnetics Association Annual Technical Report.
- Aspect Ratio and Pull Force for Rare Earth Magnets. (2020). DIY Magnet User Group Technical Paper.
- Flux Leakage in Compact Permanent Magnet Designs. (2019). IEEE Transactions on Magnetics.
Xiamen Zhaobao Magnet Co., Ltd.
As one of the leading neodymium magnet manufacturers and suppliers in China, we have world-leading production equipment and strong manufacturing capabilities. Please rest assured to wholesale high quality neodymium magnet at competitive price from our factory. Customized orders are welcome.
Address: Room 201, No.15, Longxinli, Siming District, Xiamen, Fujian, China
E-mail: zb16@magnets-world.com
WebSite: https://www.magnet-king.com/
