Recommended units

In view of the confusion with regard to the units sometimes seen in our journals, the Editorial Committee of the Magnetics Society of Japan has decided to present a recommendation concerning the units to be used in the journals. We propose the international system of units (SI) as the recommended system of units in our journals, in accordance with international trends. Regrettably, however, the change over to SI has been slower in the field of magnetism than in other fields. In view of this situation, we recommend SI but do not refuse to accept the use of other unit systems such as the cgs unit system. However, mixed use of them should be avoided. We ask you to use SI units with reference to the conversion tables below (Tables 1 to 3).

Table 1 Conversion table to SI for magnetism related properties.

Quantity Symbol cgs-Gauss
( B =
H + 4M)
factor to SI
MKSA units
(E-H cor.) B=
0 H + I
to SI
(E-B cor.)
0 (H + M ))
Magnetic flux density B G 10-4 T, Wb/m2 1 T, Wb/m2
Magnetic flux Mx 10-8 Wb 1 Wb
Magnetomotive force Vm Gb 10/4 A 1 A
Magnetic field strength H Oe 103/4 A/m 1 A/m
Magnetization M, I emu/cm3 103 Wb/m2 1/0 A/m,
Mass magnetization emu/g 1 (Wbm)/kg 1/0 Am2/kg
Magnetic moment m emu 10-3 Wbm 1/0 Am2,
Susceptibility -,
4 H/ma 1/0 -b
Permeability of vacuum 0 1 4 × 10-7 H/m 1 H/m
Permeability 4 × 10-7
H/m 1 H/m
Demagnetizing factor N c 1/4 d 1 e
Maximum energy product (BH)max GOe 10-1/4 J/m3 1 J/m3
Energy density E, K erg/cm3 10-1 J/m3 1 J/m3


a I=H. r defined byr =/0 is equal to  in SI.
b M=H
c Nx + Ny + Nz= 4p
d Demagnetizing field:Hd= – (N/0)I, Nx + Ny + Nz = 1
e Demagnetizing field:Hd= –N M,Nx + Ny + Nz = 1

Table 2 Conversion table for inch-unit quantities used in magnetic and optical recording.

Quantity Inch-unit Conversion factor
to recommended unit
Recommended unit f Notes
recording density
bpi, frpi, fci 100/2.54 bit/m, fr/m, fc/m Use
prefix as Mfr/m g
recording density
bit/in2 104 / 6.45 bit/m2 Use
prefix as Tbit/m2 g

f These are not SI units.
g bit/mm, fr/mm and bit/mm2 are also used.

Table 3 Conversion table for quantities that should be expressed in SI.

Quantity Unit Conversion factor
to recommended unit
Recommended unit Notes
Length A 0.1 nm Temporary use in SI units
Pressure Torr, mmHg 133.322 Pa

Others; The use of day (d), hour (h), and minute (min) along with “s” in SI, and of plane angles of degree ( ° ), minute ( ´ ), and second ( ” ) along with “rad” in SI is authorized internationally, and therefore there is no need to take the trouble to convert them into SI.

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