"How many gauss is your magnet?" is the most common question in magnet sourcing — and the hardest to answer, because gauss can mean three different things. Surface field belongs to the object, remanence to the material, and flux to the application. Mixing them up leads to wrong comparisons and failed specs.
Surface field — the property of the object
Surface field is what a gaussmeter reads when you touch the probe to one point on the magnet. It depends on the magnet's shape and size, and on exactly where you measure. A big, weak ferrite block can measure a higher surface field than a small, powerful N52 cube. It is a point measurement of an object, not a material rating.
Remanence — the property of the material
Remanence (Br) is the strength a material keeps after being magnetized, regardless of shape or size. One grade, one Br. This is the number to use when comparing materials — see the four key parameters.
Flux — what the application actually uses
Flux is the total field passing through a surface — roughly, field strength times area. It is what your product actually feels: pull force, motor torque and sensor signals all scale with flux. Factories measure it with a fluxmeter and a Helmholtz coil, which integrates the whole magnet in one pass.
Why it matters
| Quantity | What it is | Depends on | Use for |
|---|---|---|---|
| Surface field | Field at one surface point | Shape, size, probe position | Quick in-line checks |
| Remanence | Material's retained strength | Material only | Comparing materials |
| Flux | Total field through a surface | Magnet + geometry | Batch QC, design |
Compare materials by grade (Br, (BH)max), check production parts by flux or moment, and treat surface gauss as a quick same-shape comparison only.
Read on: the hysteresis loop → · magnetic moment vs. flux →