Maximum energy product
Maximum energy product, written (BH)max, is a key measure of a permanent magnet’s strength. It is given in kJ/m3 or MGOe (1 MGOe = 7.958 kJ/m3). In the 20th century, magnet materials improved from about 1 MGOe to over 50 MGOe with neodymium magnets. Other important properties are remanence (Br) and coercivity (Hc), which come from the same B–H loop but are not the same as (BH)max.
(BH)max is found on the demagnetizing portion of the B–H curve, where B and H oppose each other. It is the maximum value of −BH along that curve, which can also be pictured as the largest rectangle that fits from the origin to the demagnetization curve.
The practical point is that a higher (BH)max lets you make a smaller magnet for the same magnetic field. In a simple setup with a magnet, an air gap, and a core, the energy in the gap is tied to −BH in the magnet. To achieve a target field in the gap, you maximize −BH and shape the magnet so that −BH equals (BH)max, which minimizes the magnet’s volume. This assumes the core has very high permeability; in real cores, saturation eventually limits the flux.
This page was last edited on 3 February 2026, at 08:48 (CET).