Magnetic Field Strength Converter
Convert magnetic field strength (the H field) between ampere per meter, ampere-turn per meter, kiloampere per meter and oersted. Pick a source and a target unit, enter a value and read the result instantly.
Select two units to see the conversion factor.
Magnetic field strength H (A/m, oersted) is not magnetic flux density B (tesla, gauss). Although 1 Oe corresponds to 1 G in a vacuum, this tool never converts between H and B.
Magnetic Field Strength Formula
Every field strength unit is a fixed multiple of one reference unit, the ampere per meter (A/m). To convert, multiply the value by the size of the source unit in A/m, then divide by the size of the target unit in A/m. The ampere-turn per meter equals the ampere per meter, the kiloampere per meter is 1,000 A/m and the oersted is exactly 1000 ÷ (4π) A/m, about 79.57747 A/m.
What Is Magnetic Field Strength?
Magnetic field strength, written H, describes the magnetizing effect of electric currents, independent of the material that the field passes through. For a long solenoid it equals the number of turns times the current divided by the length: H = N × I ÷ l. In other words it is magnetomotive force per unit length, and its SI unit is the ampere per meter (A/m). Because a turn is a count, ampere-turn per meter is the same unit as ampere per meter.
The CGS unit is the oersted (Oe), equal to 1000 ÷ (4π) A/m, about 79.577 A/m. Magnetic-materials data, such as the coercivity of a permanent magnet, are often given in oersted or kA/m.
H is different from B. Magnetic flux density B is the resulting field, measured in tesla or gauss, and in a material it follows B = μ × H, with μ = μ₀μᵣ. In a vacuum (and approximately in air) μ is about 4π × 10⁻⁷ H/m, which is why a field strength of 1 Oe corresponds to a flux density of 1 G there. In a magnetic material the permeability is different, so the correspondence no longer holds. For that reason the converter keeps H and B separate and only converts between H units.
Supported Units
This converter supports the following 4 magnetic field strength units. The last column shows how many amperes per meter one unit equals.
| Unit | Symbol | Value in A/m |
|---|---|---|
| Ampere per meter | A/m | 1 |
| Ampere-turn per meter | At/m | 1 |
| Kiloampere per meter | kA/m | 1,000 |
| Oersted | Oe | 79.57747155 |
How to Use the Magnetic Field Strength Converter
- Type the magnetic field strength in the value box. Decimals and scientific notation such as 0.0025 or 2.5e-3 are accepted.
- Choose the From unit and the To unit.
- The result appears instantly, or press Convert Now. Very large or very small results are shown in scientific notation.
- Use Swap Units to reverse the conversion, Copy Result to copy the answer, open Show this value in all units for a full list, and Clear to start again.
Step-by-step by hand
- Find the size of each unit in the common base unit (A/m): 1 Oe = 79.57747155 A/m and 1 A/m = 1 A/m.
- Divide the source size by the target size to get the conversion factor: 79.57747155 ÷ 1 = 79.57747155, so 1 Oe = 79.57747155 A/m.
- Multiply by your value: 1 Oe × 79.57747155 = 79.57747155 A/m.
Field strength cannot be negative in this tool, so only zero and positive numbers are accepted; the sign of H only gives its direction.
Common Field Strength Conversions
- CGS to SI: 1 Oe equals 79.57747155 A/m.
- Permanent-magnet data: a coercivity of 12 kA/m equals 150.7964474 Oe.
- Solenoid: 500 turns carrying 2 A over 0.5 m gives H = 500 × 2 ÷ 0.5 = 2,000 At/m, which is 2 kA/m or 25.13274123 Oe.
- Weak field: 40 A/m equals 0.5026548246 Oe.
- Small oersted values: 0.5 Oe equals 39.78873577 A/m.
Oersted to Ampere per Meter – Common Values
Quick reference for frequently used values
| Oersted | Ampere/meter | Kiloampere/meter |
|---|---|---|
| 0.1 | 7.957747155 | 0.007957747155 |
| 0.5 | 39.78873577 | 0.03978873577 |
| 1 | 79.57747155 | 0.07957747155 |
| 5 | 397.8873577 | 0.3978873577 |
| 10 | 795.7747155 | 0.7957747155 |
| 50 | 3,978.873577 | 3.978873577 |
| 100 | 7,957.747155 | 7.957747155 |
| 500 | 39,788.73577 | 39.78873577 |
| 1,000 | 79,577.47155 | 79.57747155 |
Where and Why This Conversion Is Used
- Magnetic materials and magnets: coercivity and magnetizing fields are quoted in A/m, kA/m or oersted, depending on the source.
- Magnetic recording and sensors: head and sensor fields, and the fields applied to test them, appear in oersted in older literature.
- Electromagnet and solenoid design: H = NI ÷ l is evaluated in A/m.
- Geophysics and shielding: field strengths are compared in SI and CGS units.
Important Differences Between Related Magnetic Quantities
- Magnetomotive force, F (ampere-turn, gilbert): the “driving force” of a magnetic circuit, F = N × I.
- Magnetic field strength, H (A/m, oersted): magnetomotive force per unit length of the magnetic path.
- Magnetic flux density, B (tesla, gauss): how strong the resulting magnetic field is, and the flux per unit area. In a material B = μ × H.
- Magnetic flux, Φ (weber, maxwell): the total magnetic field passing through an area, Φ = B × A.
These four quantities have different dimensions, so none of them can be converted into another by a unit factor. Moving between them needs extra information such as a length, an area or the permeability of the material. Each converter here only changes units within one quantity. See the Magnetomotive Force Converter, Magnetic Field Strength Converter, Magnetic Flux Converter and Magnetic Flux Density Converter.