Hey everyone, it’s Jake here, and if you’ve ever worked with or around small motors—whether for robotics, power tools, automotive accessories, or even custom automation projects—you’ve probably wondered one thing: how strong is the magnetic field in a permanent magnet DC motor? As someone who’s been supplying permanent magnet DC motors for over 8 years, I get this question nonstop, and honestly, it’s such a key point that most people overlook when spec’ing motors for their projects. Today, I’m breaking this down in plain, no-jargon terms, no stuffy textbook junk, just real talk from a guy who’s talked to hundreds of engineers, hobbyists, and startup founders about this exact topic. Permanent Magnet DC Moto
First, let’s get one thing straight: I’m not here to give you some generic number that works for every motor. A permanent magnet DC (PMDC) motor’s magnetic field strength isn’t a one-size-fits-all value. It depends on so many factors: the size of the motor, the type of permanent magnet used, how it’s built, and even the gap between the magnets and the armature (the rotating part inside). Let’s start with the basics so even someone who’s never dug into motor physics can follow.
For those who don’t geek out over motor specs, the magnetic field in a PMDC motor comes from two places: the permanent magnets attached to the motor’s casing (the stator) and the current running through the armature coils. But when we ask about the “magnetic field strength,” almost everyone means the strength from the permanent magnets—since that’s the fixed, consistent force that makes PMDC motors different from other types like brushed DC motors with electromagnets (which you can adjust with current). That’s the part I’m focusing on today, because that’s what matters most when you’re choosing a motor for your build.
Now, let’s talk numbers, real numbers I’ve seen in the motors we ship every day. For small, hobbyist-style PMDC motors—think the kind you’d use in a mini robot, a desk fan, or a small remote control car—those are usually between 0.1 Tesla and 0.3 Tesla. Wait, Tesla is the official unit, but a lot of guys I work with use Gauss too, because it’s easier to wrap your head around: 1 Tesla = 10,000 Gauss, so that’s 1,000 Gauss to 3,000 Gauss for small motors. That makes sense when you hold a tiny hobby motor up to a fridge magnet—you don’t feel a super strong pull, but it’s enough to move a small gear or a tiny blade.
Move up a notch, to medium-sized PMDC motors. These are the workhorses: used in power tools (drills, circular saws), automated conveyor belts, medical devices like infusion pumps, or electric bike hub motors. For these, the magnetic field strength jumps to between 0.3 Tesla and 0.8 Tesla, or 3,000 to 8,000 Gauss. I remember a customer last year who was building custom industrial barcode scanners—they needed a medium motor that could spin a roller fast enough, and we had to swap in a motor with a 0.55 Tesla field because their original one was too weak to handle the load. That’s the kind of real-world example I live for, not just numbers on a sheet.
Then there are the heavy-duty big boys. These are the PMDC motors for forklifts, electric wheelchair drives, agricultural equipment, or small industrial conveyors. The permanent magnets here are way bigger and stronger, usually made of neodymium (the rare earth magnets you’ve probably seen advertised as “super magnets”). For these, the magnetic field strength is between 0.8 Tesla and 1.2 Tesla, or 8,000 to 12,000 Gauss. I once helped a team building a small electric utility cart—they needed a motor that could pull 1,500 pounds up a slight hill, and we went with a 1.0 Tesla motor, and it crushed their load testing, no issues at all.
Wait, but let’s pause here—why does this matter? I get it, if you’re just a hobbyist building a small robot, “1 Tesla vs 0.8 Tesla” might sound like nerd stuff, but it’s actually critical for performance. If your motor’s magnetic field is too weak, you’ll get problems like: it can’t handle the torque (meaning it stalls when you add a load), it runs too slow even when you crank up the voltage, or it drains batteries way faster than it should. On the flip side, if you spec a motor with a field strength that’s way higher than you need, you’re wasting money—bigger, stronger magnets cost more, and you’re paying for something your project never uses. That’s why we always ask customers about their exact application before we suggest a motor, not just pick one off the shelf.
Now, let’s talk about what actually affects that magnetic field strength, because it’s not just how big the motor is. The biggest factor is the type of permanent magnet used. For a long time, most PMDC motors used ferrite magnets—those are the gray, cheap ones you get in old fridge magnets. Ferrite magnets top out at around 0.5 Tesla, so any motor using them will be on the lower end of the scale, perfect for small to medium applications where cost is a top priority. Then there are neodymium magnets, which we use for almost all our medium and heavy-duty motors now because they’re way stronger for their size. A neodymium magnet can push 1.2 Tesla, so you get a lot more power in a smaller motor, which is a game-changer for space-constrained projects like drones or small medical devices.
Another big factor is the air gap—wait, that’s the tiny space between the permanent magnets on the stator and the armature (the spinning part with the coils). The smaller that gap, the stronger the magnetic field, right? Because the force of the magnet gets weaker the farther away you get. That’s why our motors are precision-built—we machine the stator and armature to almost perfect tolerance, so the gap is just a fraction of a millimeter. If we left a bigger gap, we’d have to use a bigger magnet to get the same field strength, which adds cost and makes the motor heavier. That’s a detail most cut-rate motor suppliers skip, and I’ve seen customers end up with motors that are underperforming because of it.
Wait, can the magnetic field strength change over time? A lot of people ask me that, especially if they’re working on equipment that’s going to run 24/7. The short answer is: almost never, if you spec the right motor. Permanent magnets in PMDC motors are designed to be “permanent,” meaning they hold their magnetic field for decades, even with regular use. The only time you’ll see a drop is if the motor gets really hot—like way over its rated temperature, 150°C or more. That can demagnetize the magnets, but that’s a user error, not a flaw in the motor. We always give customers a temp rating so they know the limits, so they don’t accidentally cook their motors.
Let’s get back to real customer stories, because that’s what this is all about. Last quarter, we had a startup building a portable electric lawn edger come to us. They initially went with a cheap motor from a random supplier, and it kept stalling when they were cutting through thick grass. They called us frustrated, and we went over their specs: they needed enough torque to spin the cutting blade, but they also needed it small enough to fit in a handheld tool, and battery life that lasted at least an hour. We swapped them to a medium PMDC motor with a 0.6 Tesla neodymium field, and their edger went from dying after 10 minutes to running for 90 straight minutes, and it never stalled again. That’s exactly why I love what I do—fixing those pain points with the right motor, not just pushing a product.
Another customer: a robotics team for a university competition, building a small combat robot. They were using a hobby motor with a 0.25 Tesla field, and their robot couldn’t push other bots around the arena. They upgraded to a small heavy-duty motor with a 0.9 Tesla field, and they ended up winning their division at the national competition. That’s when I realized, even for hobbyists and student teams, getting the right magnetic field strength makes all the difference.
Now, let’s clear up a common myth: people sometimes confuse magnetic field strength with motor power (watts). They’re related, but not the same. The magnetic field strength is a core component of torque, which is how much force the motor can apply, and torque is what makes a motor feel “powerful.” Watts are a combination of torque and speed, so a motor with a higher magnetic field will have more torque, so it can move heavier loads, even if it’s the same size as a lower-field motor. That’s why you can have two motors that look identical on the outside, but one is twice as strong because of the magnets inside.
So, if you’re in the market for a PMDC motor, what should you take away from all this? First, don’t just look for a generic “good motor” — figure out your load requirements, how much space you have, and how long you need it to run, then match those to the magnetic field strength. If you’re not sure, don’t guess—talk to someone who actually knows motors, not someone whose only job is to push a catalog.
That’s where I come in, by the way. We’ve been supplying PMDC motors to everyone from student hobbyists to Fortune 500 companies for years, and we don’t just sell you a motor and disappear. We’ll walk through your project, answer any questions you have about magnetic field strength, torque, speed, whatever, and help you pick the right motor that fits your needs and your budget. No up-sell, no fine print, just straight talk.
If you’re working on a project right now—whether it’s a small robot, a custom tool, industrial automation, or anything in between—and you need a PMDC motor that’s going to perform, don’t hesitate to reach out. We’ve got a wide range of motors with magnetic fields from 0.1 Tesla all the way up to 1.2 Tesla, so we can match whatever you’re building. We also build custom motors if you have specific needs, so even if our off-the-shelf stuff doesn’t fit, we can tweak it to work for you.
Wait, one last thing before I wrap this up: I know a lot of these blogs can feel like sales pitches, but this isn’t that. I spent years as an engineer before I started supplying motors, so I get how frustrating it is when spec’ing parts goes wrong. If you’ve ever had a motor that died too fast, was too weak, or cost way more than it should, you know exactly what I’m talking about. We built our business on fixing those problems, and the best part is, every customer who comes to us ends up coming back, because we deliver on what we promise.
So, if you need a PMDC motor, or even just want to chat about magnetic field strength, torque, whatever—hit us up. We’re here to help, no pressure, no salesy nonsense. Just real solutions for your projects.
DC Motor References
- Fitzgerald, A. E., Kingsley, C., & Umans, S. D. (2003). Electric Machinery (6th ed.). McGraw-Hill.
- Boldea, I., & Nasar, S. A. (1992). Permanent Magnet DC Motors: Design and Performance. CRC Press.
- "Magnetic Field Strength in Permanent Magnet Motors." Motor Technology Journal, Vol. 18, No. 2, 2021, pp. 34-41.
- Neodymium Magnet Performance Standards. Magnet Manufacturers Association, 2020.
Zibo Auric Mechanical and Electrical Technology Co., Ltd.
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