One MGOe equals 7.958 kJ/m³, so the conversion is BHmax (kJ/m³) = BHmax (MGOe) × 7.958 [S2][S7].
The factor converts the maximum energy product of permanent magnet material from the CGS unit megaGauss-oersted to the SI unit kilojoule per cubic metre, commonly written kJ/m³ [S3][S4].
The conversion factor and worked examples
The exact working relationship is 1 MGOe = 100 ÷ 4π kJ/m³ ≈ 7.958 kJ/m³ [S7]. Magnetic-unit references give the conversion as 1 MGOe = 100 ÷ 4π kJ/m³ ≈ 7.958 kJ/m³ [S2][S4][S10].
Multiplying by 7.958 preserves the value while changing its units. A grade designation of N42 represents a nominal BHmax of about 42 MGOe, which converts to 42 × 7.958 = 334.236 kJ/m³, normally rounded to 334.2 kJ/m³ [S5][S7]. An N52 grade converts from about 52 MGOe to 413.8 kJ/m³ [S1][S7].
What BHmax represents in magnet material
BHmax is the largest value of the product B·H along the material's demagnetization curve, with B expressed in tesla and H in amperes per metre when the result is stated in kJ/m³ [S2][S9]. It quantifies the maximum magnetic energy that can be stored per unit volume of magnet material at the operating point corresponding to that curve maximum [S2].
Maximum energy product is a material characteristic, not a measurement of surface flux density. Magnet manufacturers use it to compare permanent magnet grades and material families, including sintered neodymium magnets [S2][S5]. A grade number such as N42 denotes nominal maximum energy product in MGOe, not the magnet's residual induction or surface field in gauss [S5][S7].
That distinction matters during specification. A magnet can have a high BHmax while producing a lower surface field because geometry, working direction, pole shape, air gap and material volume affect the external field. The energy meter reference is separate instrumentation and does not measure BHmax, so it should not be used to validate this material-property conversion.
Method for procurement and engineering calculations
Enter the supplier's BHmax value in MGOe, multiply it by 7.958, and report the result in kJ/m³ with a sensible number of significant figures. For 42 MGOe, the conversion is 334.2 kJ/m³; for 52 MGOe, it is 413.8 kJ/m³ [S5][S7]. Dividing a kJ/m³ value by 7.958 reverses the operation.
Use the unrounded factor of 7.958 during intermediate arithmetic and round only the final result. The rounded factor 7.96 introduces a small relative difference: for 50 MGOe, 7.958 produces 397.9 kJ/m³, while 7.96 produces 398.0 kJ/m³ [S2][S4][S7][S10].
For grade-to-grade screening, 30 MGOe converts to 238.74 kJ/m³, 35 MGOe to 278.53 kJ/m³, 40 MGOe to 318.32 kJ/m³, and 45 MGOe to 358.11 kJ/m³. A grade comparison in SI units therefore preserves the same ordering as the original MGOe values because the conversion factor is constant.
Where MGOe and kJ/m³ fit in a specification
MGOe is the conventional CGS unit used in magnet grade names and supplier catalogues, while kJ/m³ is the SI unit used in academic work, engineered magnetic-circuit calculations and material comparisons [S3][S10]. N42 has a nominal maximum energy product of about 42 MGOe, which is approximately 334 kJ/m³ [S5][S7].
The units should not be confused with magnetic flux density or field strength. Magnetic flux density B is expressed in tesla, with 1 T = 10,000 G; field strength H is expressed in A/m or oersted, with 1 Oe corresponding to approximately 79.577 A/m; and the maximum energy product combines B and H into a volume-based energy density [S1][S2].
For purchased components, require the material grade and manufacturer-declared nominal BHmax, rather than inferring material performance from a measured surface-field reading. Surface flux measurements and power meter readings answer different physical questions, while clamp meter measurements concern electric current. None provides a direct conversion between MGOe and kJ/m³.
Limits, rounding and interpretation
The conversion changes the unit, not the measurement conditions or tolerance. If a datasheet specifies 42 ± 2 MGOe, the same nominal band is 334.236 ± 15.916 kJ/m³, or 334.2 ± 15.9 kJ/m³ after rounding [S2][S7]. A grade label such as N42 or N52 is a nominal grade identifier rather than a guaranteed minimum for every production unit [S5][S7].
BHmax is also not interchangeable with coercivity or operating temperature. Those are separate magnet properties, and the maximum energy product alone does not specify pull force, magnetic flux at a defined gap, corrosion resistance, coercivity or permissible service temperature. For assemblies, the earth-ground tester and high-voltage tester can address electrical bonding or insulation checks, but neither determines BHmax.
The strongest commercially available magnetic material has a maximum energy product of around 52 MGOe [S8]. This value is a material benchmark for conversion work, not proof that every N52 magnet delivers identical external magnetic performance.
The next specification check is straightforward: confirm that the datasheet labels the value as maximum energy product, read the MGOe figure, apply 7.958, and record the result in kJ/m³. Keep the original MGOe value alongside the converted SI value so the grade remains traceable [S2][S3][S7].