How Strong Is a Rod Magnet Really? And why doesn’t it just keep getting stronger the longer it gets?
When working with rod magnets, it’s natural to think: “If I make the magnet longer, it’ll get stronger too, right?” – but it’s not quite that simple.
It may seem strange that disc magnets with axial magnetization continue to increase in strength by more than 50% as they get taller, while rod magnets don’t gain strength in the same way as they get longer.
That’s because increasing the height improves the depth of the magnetic field, but it doesn’t significantly increase the pulling force of the magnet once it becomes taller than its diameter. The most important factor for pulling power is the surface area of the magnet’s end face.
What’s the difference between a disc magnet and a rod magnet?
- A disc magnet is defined by having a height that does not exceed its diameter – for example, 5×5 mm or 10×10 mm.
- A rod magnet is defined by having a length (or height) greater than its diameter – for example, 5×7 mm or 10×12 mm and upwards.
This means, for example, that a rod magnet in size 5×10 mm won’t be significantly stronger than a 5×5 mm magnet. But a 5×2 mm magnet compared to a 5×4 mm magnet will show a strength increase of over 50%, whereas the 5×10 mm magnet only increases strength by a little over 20%:
- 5×5 mm disc magnet (N45 NdFeB): approx. 900 grams
- 5×10 mm rod magnet (N45 NdFeB): approx. 1,100 grams
That means: doubling the height only gives you around 22% more pulling strength.
Can a magnet become stronger at all?
Yes – the N-value (magnet grade or density) can be increased. Most of our magnets are made in N45 and N48. Compared to those, an N50 magnet of the same size will typically be about 5–7% stronger than an N48.
We know it can get a bit technical if you’re not working with magnets and magnetism daily, so here’s a simple breakdown:
What determines the strength of a rod magnet?
The pulling force (i.e., how strongly a magnet sticks to a steel plate) depends primarily on:
- The surface area of the end face – larger diameters provide more contact and magnetic force.
- Magnet quality (e.g. N35 vs. N50) – higher numbers mean stronger magnetic fields.
- Length – but only up to a certain point.
It also matters a great deal what kind of surface the magnet is attached to – a clean, thick metal plate in high quality will provide much better performance than a thin steel sheet or a glass board (where the glass creates a gap between magnet and steel).
In our calculations, we always assume a clean, ideal metal surface so you can compare values on equal terms.
The limits of magnet length
When you increase the length of the magnet, the magnetic field becomes a bit deeper and the total energy increases – but the pulling force only increases slowly. That’s because the magnetic field mostly loops inside the magnet and exits through the end face – and if that face doesn’t get larger, the field can’t be released much more effectively.
Greater length = slightly more reach and stability, but only a small increase in pull force.
When is a longer rod magnet useful?
- When you need a deeper magnetic reach – for example in sensors or drawer mechanisms.
- When you want to prevent the magnet from tipping (a longer shape is more directionally stable).
- When you’re limited in width, but there’s room to work with in height.
Feel free to reach out if you'd like help with your magnet project – we've been working with neodymium magnets since 2011.
