Magnetic Field Strength Converter
Magnetic field strength, the H field, is measured in the SI unit of amperes per meter (A/m). The CGS unit is the oersted, where one oersted equals 1,000 divided by 4 pi amperes per meter, about 79.577 A/m. This converter handles A/m, A/cm, kA/m, and the oersted, reducing each to amperes per meter as a common base. Note that this is the magnetizing field H, not the magnetic flux density B (measured in tesla or gauss), which is a separate quantity.
Magnetic field strength conversion
Base value (A/m) = input * factor(from unit)
Output = base value / factor(to unit)
1 A/cm = 100 A/m
1 kA/m = 1,000 A/m
1 Oe = 1000 / (4 pi) A/m = 79.5774715 A/m
The oersted is the CGS-Gaussian unit of H. Its conversion uses the factor 1000 divided by 4 pi, which is exact in terms of pi.
Magnetic field strength context
- The SI unit of magnetic field strength (H) is the ampere per meter (A/m).
- The oersted is the CGS unit, equal to 1000 divided by 4 pi A/m, about 79.577 A/m.
- H (field strength) differs from B (flux density), which is measured in tesla or gauss.
- In a vacuum, B in tesla equals the magnetic constant times H in A/m.
- The H field is set by free currents through Ampere's law.
Magnetic field strength: frequently asked questions
What is the difference between H and B?
H is the magnetic field strength (A/m), set by free currents. B is the magnetic flux density (tesla or gauss), which includes the material's magnetization. They are related by B = mu times H. This converter handles H.
How many A/m are in an oersted?
One oersted equals 1000 divided by 4 pi amperes per meter, which is about 79.5775 A/m. The factor comes from the CGS-Gaussian definition of the oersted.
Why does the oersted factor contain pi?
The CGS-Gaussian system defines the oersted so that converting to SI introduces a factor of 4 pi, a consequence of how the two systems handle the magnetic constant. Hence 1 Oe is 1000 over 4 pi A/m.
Is the oersted the same as the gauss?
No. The oersted is the CGS unit of magnetic field strength H, while the gauss is the CGS unit of flux density B. They are numerically equal only in a vacuum under the Gaussian convention.
How do I convert kA/m to A/m?
Multiply by 1,000, since a kiloampere is 1,000 amperes. So 1 kA/m equals 1,000 A/m.
Official sources
- NIST Special Publication 811: Guide for the Use of the International System of Units.
- NIST Office of Weights and Measures: SI Units.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.