Magnetism Converter

This unified converter handles the four most common quantities in magnetism: magnetic flux density (also called B-field, measured in tesla or gauss), magnetic flux (weber or maxwell), magnetic field strength (also called H-field, measured in amperes per metre or oersted), and magnetomotive force (ampere-turn or gilbert).

Pick the quantity at the top, then convert between its SI and CGS units. The four are deeply related — flux equals flux density times area, flux density is field strength times permeability, magnetomotive force drives flux around a magnetic circuit — but each has its own units and use cases.

Flux density is quoted in tesla in SI and in gauss in the older CGS system, and the relationship is a clean factor of ten thousand: one tesla is 10,000 gauss. Both remain in active use, which is why a figure can look wildly different depending on which literature it came from.

The two units suit different scales. The Earth's magnetic field is around 50 microtesla, which is a more manageable 0.5 gauss — so geophysics and small-field work favour gauss. A clinical MRI at 1.5 tesla is 15,000 gauss, where the SI figure is clearly the more usable one.

• Flux and flux density are different quantities: the weber measures total flux, the tesla measures flux per unit area.
• The maxwell is the CGS unit of flux, at 10⁻⁸ weber, so one weber is 100 million maxwells.
• A tesla is also a weber per square metre and a volt second per square metre — the same quantity written three ways.

Magnetics uses two field quantities that are easy to confuse because both are called "the magnetic field" in casual speech. B is flux density, measured in tesla or gauss. H is field strength, measured in amperes per metre or oersteds, and this converter handles both.

The distinction is that H describes the field a current or magnet applies, while B describes what actually exists in the material once the material's own response is included. In a vacuum they are proportional; inside iron they are not, because the material contributes enormously. That is precisely what makes transformer cores and electromagnets work.

• One oersted is about 79.577 amperes per metre — the factor is 1000/4π, which is why it is not a round number.
• Magnetomotive force, measured in ampere-turns or gilberts, is the magnetic analogue of voltage driving flux around a circuit.
• The relationship between B and H in a real material is not a constant, so it cannot be converted — it is a curve, and it depends on history as well as the present field.