"How many gauss?" is usually the first question buyers ask about a magnet — and one of the easiest to get wrong. A gaussmeter (also called a teslameter) measures the magnetic field at a single point on the surface. It is fast and cheap. Used well it is a great quick check; used carelessly the numbers cannot be compared between suppliers.
How does it work?
Inside the probe sits a tiny sensor chip. When you hold it in a magnetic field, the field pushes electrons in the chip sideways and creates a small voltage. The bigger the field, the bigger the voltage — and the meter converts it into a reading in gauss or tesla (1 tesla = 10,000 gauss). This is called the Hall effect.
Which probe, and where?
Most probes are flat and sense the field straight through the chip — the right choice for flat pole faces. Axial probes, which sense along their tip, are for holes and gaps. On small magnets, use the smallest probe you can: a large chip averages the field over a wide area.
Why different positions give different numbers
The confusing part: the field across one magnet face is not uniform. Magnetic flux crowds toward corners and edges, so a reading at the edge can be much higher than one at the center. Move the probe a few millimetres and the number changes.
That is why factories always measure at a fixed, agreed point — usually the center of the pole face. Magnetization direction matters too: a magnet magnetized along a different axis reads differently on the same face.
One more thing to remember: surface field belongs to the object, not the material. Two magnets of the same grade with different shapes read differently. Compare only magnets of the same shape, measured at the same point, with a similar probe.
Read on: why coil-based flux and moment tests are more reliable → · surface field vs. remanence vs. flux →