If you want to know how strong a magnet really is, the gaussmeter is not the best tool. A single surface reading changes with probe position, probe size and even the person holding it. Flux and magnetic moment measure the whole magnet at once — which is why wind-turbine and EV manufacturers release their magnets on these numbers instead.
What are flux and moment?
Flux is the total amount of magnetism flowing through an area. It is the number your application actually consumes: force, torque and induced voltage all grow with it. Magnetic moment is a related idea — a single number that describes how strongly the magnet acts as a magnetic source, whatever its shape.
How the coil method works
You cannot read flux with a probe. Instead, factories use coils: the magnet is dropped into or pulled through a coil, and the moving field generates a voltage pulse in the wire. A fluxmeter integrates that pulse into a flux number.
For magnetic moment, a Helmholtz coil is used — two identical coils facing each other. The magnet sits at the center and is pulled out along the axis; the flux change is directly proportional to its moment.
Why it beats a single-point reading
- Repeatable — no probe position to argue about. The same magnet gives the same number on any properly calibrated setup.
- Whole object — it captures the real strength of the part, not just one spot on the face.
- Odd shapes welcome — thin discs, arcs, rings and multi-pole parts, where surface readings scatter badly, measure cleanly.
- Fast — seconds per part, ideal for batch checks.
One caveat: numbers only compare between setups calibrated the same way, so buyers and suppliers should agree on the method and the reference magnet in advance.
Read on: how the B-H curve is measured → · surface field with a gaussmeter →