Magnet data sheets speak two dialects: SI (tesla, A/m) and CGS (gauss, oersted). Both appear on nearly every datasheet, and neither is going away. CGS grew up with the magnet industry — grades are defined in MGOe — while SI is what physics and engineering software use. Here is what each unit means.
The units, one line each
- Tesla (T) — the SI unit of flux density: how strong the field is. A strong NdFeB magnet has a remanence of roughly 1.2–1.45 T.
- Gauss (G) — the CGS unit of the same thing, used by gaussmeters and US catalogs. 1 T = 10,000 G.
- Oersted (Oe) — the CGS unit of field strength, used for coercivity. 1 Oe ≈ 79.6 A/m.
- kA/m — the SI unit of field strength as datasheets usually write it. A typical N42 has Hcj ≈ 1,590 kA/m.
- MGOe — the CGS unit of energy product. This is the number in a grade name: N42 means about 42 MGOe. 1 MGOe ≈ 7.96 kJ/m³.
The conversions you need
| Quantity | SI | CGS | Convert |
|---|---|---|---|
| Flux density | T | G | 1 T = 10⁴ G |
| Field strength | A/m | Oe | 1 Oe ≈ 79.58 A/m |
| Energy product | kJ/m³ | MGOe | 1 MGOe ≈ 7.96 kJ/m³ |
| Flux | Wb | Mx | 1 Wb = 10⁸ Mx |
A worked example: N42
A typical N42 grade: Br = 1.32 T = 13.2 kG, Hcj ≈ 1,590 kA/m ≈ 20 kOe, and (BH)max = 40 MGOe ≈ 318 kJ/m³. Same magnet, two dialects.
Memorize three factors — 10⁴ (T→G), 79.58 (Oe→A/m), 7.96 (MGOe→kJ/m³) — and most datasheet conversions take seconds. Always check the units column before comparing two data sheets: one supplier's 12 kOe and another's 955 kA/m are the same number.
Read on: the four key parameters → · the hysteresis loop →