Convert magnetic field strength (H) between ampere/metre, ampere/centimetre and oersted.
Magnetism • 6 units
All 6 units on the Magnetic Field Strength Converter are defined against the Ampere/meter (A/m), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 A/m = 0.0125663709 Oe. Change either side and every row in the table recalculates with it.
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The conversion between SI and CGS in this family carries a factor of 4π, which is why the numbers look arbitrary: one oersted is 1000/(4π) amperes per metre, or about 79.577 A/m, and one A/m is about 0.01257 Oe. That factor is a fossil of how the two unit systems distributed the constants in the magnetic equations, and it is the single most common source of error when reading permanent-magnet literature, where oersteds remain standard.
A worked case makes the scale concrete. Magnetising force from a solenoid is simply turns times current divided by length, so a 500-turn coil carrying 2 A over 0.25 m produces 4,000 A/m. Against that, a sintered neodymium magnet of N42 grade has an intrinsic coercivity of at least 12 kOe — about 955 kA/m — which is why demagnetising such a magnet requires a field hundreds of times stronger than an ordinary coil delivers, and why they survive handling that would wipe a weaker material.
Ampere-turns per metre and amperes per metre are listed separately in the table but are numerically identical, and the redundancy is deliberate: the ampere-turn form reminds you that turns are a pure count and carry no unit of their own. The distinction that does matter is the one between this quantity and flux density in teslas. H is what the current applies; B is what the material returns, and the ratio between them is not a constant inside iron. Converting H correctly and then treating it as B is a much larger error than any unit slip.
Quick reference — 1 Ampere/meter (A/m) is equal to:
| Ampere/centimeter | A/cm | 0.01 |
| Kiloampere/meter | kA/m | 0.001 |
| Oersted | Oe | 0.0125663709 |
| Ampere-turn/meter | At/m | 1 |
| Ampere-turn/inch | At/in | 0.0253999992 |
6 units of magnetic field strength, each a fixed multiple of the A/m. The table spans 1,000:1, from A/m (1 A/m) to kA/m (1000 A/m). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 A/m = 1 A/m1 A/cm = 100 A/m1 kA/m = 1000 A/m1 Oe = 79.5775 A/m1 At/m = 1 A/m1 At/in = 39.3701 A/mwhere:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 A/m = 0.314159 Oe
Magnetic field strength H, in amperes per metre (A/m), describes the magnetising effort applied to a material — the field the current produces. It is deliberately distinct from flux density B, in teslas, which describes what the material does in response.
Keeping the two apart is the whole point. In free space they are proportional, so the Earth's field of about 50 µT corresponds to roughly 39.8 A/m, but inside iron the same H produces a far larger B, and beyond saturation further H produces almost none. The CGS unit, the oersted, equals about 79.58 A/m and remains common in permanent-magnet datasheets, where coercivity is still routinely quoted in oersteds rather than SI.