Friends who are exposed to magnetic materials often encounter various  electrical or magnetic units, and since electromagnetism uses gauss unit in addition to the usual international ones, this gives us a sense of the complexity of the units of electromagnetism. For example Hcj, there are different ways of describing it in the two systems of units, 960KA/m in SI is 12KOe in CGS. Today we will take you together to summarize the units in electromagnetism and the conversion between different systems of units.

What is the system of units?

Various physical quantities are related to each other through equations that describe the laws of nature and equations that define new physical quantities. In order to develop the system of units and introduce the concept of dimensions, a group of mutually independent physical quantities and their units are usually selected as basic physical quantities and basic units, and then according to a particular set of physical formulas, selecting the proportional constant to determine the dimensions and units(derived units) of other physical quantities(derived quantity). The dimensions of the derived quantities are expressed as powers of fundamental physical quantities, derived units are expressed in basic units, some derived units have special name and symbols. Thus, the units of physical quantities form an organic rules-based whole, that is the system of units in physics.

Use different units with skill to express the formula, the best part is that you can simplify the formula a lot, reduce some complex constants to 1, so it is helpful for our derivation and understanding, that’s why there are multiple systems of units in the field of electromagnetism.

International system SI and Gaussian system CGS

The system of units of electromagnetism in the SI system is the MKSA rational system, MKSA specifies the units of the four basic physical quantities in electromagnetism, that is, the units of length、quantity、time and current intensity are respectively meters(m), kilograms(kg), seconds(s) and amperes(A).
The Gauss system of units is based on the absolute electrostatic system of units(CGSE or E.S.U) and the absolute electromagnetism CGSM of electromagnetism, the Gaussian system of units is the unified system of units which generalizes the above two systems, so it’s also called the mixed system of units. CGSE selects length, quality and time as the basic quantities, whose units are centimeter (cm), gram(g), and second(s) respectively.

Conversion relation between SI system and CGS system

The quantity of SI system multiplied by the substitution ratio of below chart  becomes the quantity in CGS system.