Pull force — also called holding force — is simply how hard you have to pull to rip a magnet off a flat steel plate. It is the number everyone quotes from datasheets, and the number everyone misunderstands.
How it is measured
Suppliers measure pull force by attaching a force gauge to the magnet and pulling it straight off (not sideways) a thick, flat steel plate, with the faces in full contact. The result is given in newtons (N) or kilograms (kg).
Two things matter. First, only ferromagnetic materials respond: iron, steel, nickel. Aluminum, brass and most stainless steel do not. Second, pull force is not a fixed property of the magnet — it depends on the target's material, thickness, surface and distance. The same magnet might hold 40 kg on a thick clean plate, and almost nothing on a thin painted sheet a few millimetres away.
Two rules of thumb
- Distance is the enemy. Pull force collapses as the gap grows. Even a coat of paint or a speck of dust between the faces measurably weakens the hold. Keep surfaces flat, clean and close.
- Close the circuit with steel. A magnet alone wastes much of its field. Put it in a steel cup (a pot magnet) or use multi-pole magnetization, and the flux is forced through the target — the same magnet suddenly pulls far harder.
A common surprise
Two identical magnets attract each other with less force than one magnet attracts a steel plate. Magnets are not good “return paths” for flux — steel is. So if your product holds magnets together, test it; do not trust the plate-rated datasheet number.
The honest takeaway
Datasheet pull force assumes a perfect thick steel plate. Real parts have gaps, coatings and imperfect surfaces. Use the datasheet to compare magnets, but run your own pull test on your real part before you commit.
Read on: magnetic circuits explained → · Pc and operating point →