What does BHmax mean?

BHmax is the maximum energy product of a magnet material, in MGOe or kJ/m³ (1 MGOe ≈ 7.96 kJ/m³). The number in N35 to N52 is the BHmax in MGOe. Neodymium reaches 33 – 53 MGOe, ferrite 1 – 4.5 MGOe.
By Team Magnetenspecialist
2 min read

Short answer: BHmax is the maximum energy product of a magnet material: the largest value of B × H on the demagnetisation curve. It indicates how much magnetic energy the material can deliver per volume. Units: MGOe or kJ/m³ (1 MGOe ≈ 7.96 kJ/m³). The number in N35, N42 or N52 is the BHmax in MGOe. Neodymium reaches 33 – 53 MGOe; ferrite 1 – 4.5 MGOe.

BHmax per material

Material BHmax (MGOe) BHmax (kJ/m³)
Neodymium N35 33 – 36 263 – 287
Neodymium N42 40 – 43 318 – 342
Neodymium N48 46 – 49 366 – 390
Neodymium N52 49 – 53 390 – 422
Samarium cobalt 16 – 32 127 – 255
AlNiCo 1.5 – 10 12 – 80
Ferrite 1 – 4.5 8 – 36
Flexible rubber magnet 0.6 – 1.5 5 – 12

What does BHmax mean in practice?

For the same magnetic performance, you need less volume the higher the BHmax. A neodymium magnet of N42 (approx. 42 MGOe) can therefore be about 10 times smaller than a ferrite magnet (approx. 4 MGOe) with the same effect. That is why electric motors, earbuds and hard drives contain neodymium magnets.

Between the neodymium grades the differences are smaller: N52 has about 50% more BHmax than N35, but that translates into about 20 to 40% more holding force. See our comparison in what do N35, N42, N48 and N52 mean?

How are Br, Hc and BHmax related?

  • Remanence (Br): how strongly the material is magnetised.
  • Coercivity (Hc): how well it holds on to that magnetisation.
  • BHmax: the combination, the usable energy. Theoretically at most about Br²/4µ₀; for Nd₂Fe₁₄B that is approx. 64 MGOe (512 kJ/m³).

On the demagnetisation curve (second quadrant of the hysteresis loop), BHmax is the point where the rectangle under the curve is largest. A magnet works most efficiently when its operating point is close to that point.

Frequently asked questions

Is a higher BHmax always better?

Not always. Grades with the highest BHmax (N50, N52) have a lower coercivity and tolerate less heat. For hot applications, an N42SH is often better than an N52.

What is MGOe?

Mega-gauss-oersted, the CGS unit of energy product. In SI units you use kJ/m³.

Read also

Need help choosing? Use the Magnet Advisor or contact us.