A/m to Oersted

How Many Oersted in an A/m?

To convert ampere per meter to oersted, divide the A/m value by 79.5775. The formula is Oe = (A/m) ÷ 79.5775 (or equivalently, multiply by 4π/1000 ≈ 0.012566). For example, 1,000 A/m equals approximately 12.57 oersted. This conversion is commonly needed when SI-based magnetic measurements must be compared with CGS datasheets or when reporting data to industries that still primarily use oersted. The permanent magnet industry, in particular, frequently specifies coercivity in oersted, and many magnetic material databases maintain dual listings in both units. Converting A/m to oersted allows seamless communication between modern research laboratories that use SI and manufacturing facilities or suppliers that reference CGS specifications. It is also helpful when older hysteresis-graph templates, gaussmeters, or purchasing documents still expect CGS-style labeling. Without the conversion, comparing lab measurements to supplier claims becomes much harder than it needs to be. Choosing between Oe and kOe after the conversion also makes a large H-field result much easier for buyers and engineers to scan. That presentation detail matters when similar magnet grades are being compared side by side.

How to Convert Ampere per Meter to Oersted

1. Start with the magnetic field strength value in ampere per meter (A/m).
2. Divide by 79.5775 to get the equivalent in oersted (Oe).
3. The result is the magnetic field strength in oersted.
4. Quick estimate: divide by 80 for an approximation accurate to about 0.5%.
5. For large A/m values in the hundreds of thousands, express the result in kilo-oersted (kOe) by dividing by 79,577.5.

Real-World Examples

History of Ampere per Meter and Oersted

The relationship between the ampere per meter and the oersted reflects one of the most contentious debates in the history of physics: the rationalization of electromagnetic units. In the early 20th century, Oliver Heaviside and others argued that Maxwell's equations should be rewritten to eliminate awkward factors of 4π from the most commonly used formulas (like Gauss's law and Ampere's law), placing them instead in formulas for point sources (like Coulomb's law). The SI system adopted this "rationalized" form, while CGS retained the "unrationalized" form. The consequence of this rationalization is that the conversion factor between A/m and oersted includes 4π, giving the seemingly arbitrary value of 79.5775 (= 1000/4π) instead of a clean power of ten. This has been a persistent source of confusion for students and practicing engineers alike. Many electromagnetic textbooks now include conversion tables specifically because these factors are so easy to misremember. Despite the mathematical elegance of SI, the oersted persists in industry because decades of accumulated magnetic materials data, standards, and equipment are calibrated in CGS units. The permanent magnet industry, which serves automotive, wind energy, electronics, and aerospace markets, still widely uses oersted for coercivity specifications.

Common Mistakes to Avoid

• Multiplying instead of dividing. To convert A/m to oersted, divide by 79.5775. Multiplying converts in the wrong direction.
• Using 10,000 instead of 79.5775. The conversion factor for field strength (H) is different from the factor for flux density (B). Tesla-to-gauss uses 10,000; A/m-to-oersted uses 79.5775.
• Dropping the factor of 4π. Some references give the conversion as "multiply by 4π × 10⁻³" — if you forget the 4π part, your answer will be off by a factor of about 12.6.
• Matching an A/m coercivity value to an oersted datasheet without checking whether the supplier means normal coercivity, intrinsic coercivity, or another H-field condition. The unit conversion may be correct while the property comparison is still wrong.

Frequently Asked Questions