Magnet Shipping Compliance Checker
Magnets are the rare industrial component that can be refused at an airport for being what they are — and the difference between an accepted tender and a rejected one is almost always packing rather than product. This tool estimates the field escaping your package at the two regulatory distances, places it in a band, and tells you what would bring it down.
interactive — estimated field at 2.1 m and 4.6 m
PI 953 classification is determined by measurement of the assembled package, rotated through 360°, using an instrument capable of resolving 0.0398 A/m within ±5 %, or by the compass method. No calculation substitutes for that. Use this tool to decide whether a shipment is obviously fine, obviously a problem, or close enough that it must be measured — and always verify against the current edition of the IATA DGR and your carrier's own policy. Anything near a threshold must be measured.
the three bands
Classification depends on the field escaping the assembled package, not on what is inside it. The same magnets pass or fail depending entirely on how they are packed — which is why this is one of the few dangerous goods classifications you can engineer your way out of at the packing bench.
| band | condition | what is required |
|---|---|---|
| unrestricted | less than 0.5° compass deflection at 2.1 m (7 ft) | Nothing beyond ordinary packaging. Ships as general cargo. |
| regulated — UN 2807 | above that floor, but not more than 2° deflection at 4.6 m (15 ft) — equivalent to 0.418 A/m (0.00525 gauss) at 4.6 m | Prior arrangement with the operator; magnetized material handling label; the words "magnetized material" and the package count in the Nature and Quantity of Goods box on the air waybill. A Shipper's Declaration for Dangerous Goods is not required. |
| above the ceiling | more than 2° deflection at 4.6 m | Transport only with prior approval of the appropriate authority of the State of origin and the State of the operator. In commercial practice carriers refuse it — the field has to be brought down. |
Field restrictions of this kind apply to air transport only. Ocean, road and rail have no equivalent threshold, although ordinary packaging and securing obligations still apply. Under the U.S. Hazardous Materials Regulations the treatment is binary rather than graduated — 49 CFR 173.21(d) makes magnetized material either not of sufficient strength to be regulated, or forbidden in transportation. The middle band above comes from the ICAO Technical Instructions and the IATA DGR, which is what governs international air movements and what carriers apply in practice.
how to bring a failing package down
Ranked roughly by effectiveness per unit of cost. Most shipments that fail need only the first two or three, and the change is usually free once it is designed into the packing method rather than improvised at the dock.
| technique | how it works | typical reduction |
|---|---|---|
| opposing orientation | Arrange magnets so adjacent poles oppose. The net dipole moment largely cancels, and what remains falls off far faster with distance than a single dipole does. | very large — usually the single biggest lever |
| keeper bars and plates | Soft iron closes the magnetic circuit so flux stays inside the assembly. Explicitly named in PI 953. | large |
| steel shielding | Steel-lined cartons or soft iron sheeting redirect and contain the field. | large; adds weight, which costs money on air freight |
| increased standoff | Centre the product with void fill so the magnets sit further from the package surface. Field falls steeply with distance. | moderate; costs dimensional weight |
| split the consignment | Fewer magnets per package means less field per package — though the carrier still sees a cumulative effect across the load. | moderate |
| ship unmagnetized | No field, no classification, no restriction. Magnetize in a fixture at final assembly. | complete — removes the question entirely |
Sintered magnets can be manufactured, machined, plated and shipped unmagnetized, then magnetized at final assembly. It removes the air cargo classification, the handling injury risk and the chipping damage from parts snapping together in transit, and it allows much denser packing. The trade is that the magnetizing fixture and the process step become yours, and it has to be agreed at RFQ stage rather than discovered later. The full treatment is in shipping magnetized material.
how the estimate works
At 2.1 metres and beyond, any practical package is magnetically a point source. The calculation therefore treats the contents as a single equivalent dipole and evaluates its field along the worst-case axis:
| dipole moment of one magnet | m = Br · V / µ₀ |
| net moment of the package | m_net = m · n · k_arrangement · k_shieldingk values above are representative, not measured |
| field on the dipole axis | B(r) = µ₀ · m_net / (2π · r³)r measured from the package centre — the measurement distance plus half the smallest package dimension |
| equivalent compass deflection | θ = arctan( H / H_earth ), H = B / µ₀, H_earth ≈ 12 A/mthe earth-field value that reproduces IATA's own stated equivalence of 2° to 0.418 A/m |
| consignment scaling | worst case ≈ single package × number of packagesfields add; IATA loading provisions note the cumulative effect explicitly |
Three things make this an estimate rather than a determination. The cancellation factors for internal arrangement are representative values, and real cancellation depends on the precise geometry of how parts sit against one another. Well-paired packing also shifts the leading term from a dipole to a faster-decaying multipole, so genuinely good packing usually measures better than this model predicts. And the consignment scaling above is deliberately pessimistic — it assumes every package reinforces every other, which only happens if they are all oriented the same way. The direction of the error is toward caution in the first and third cases, which is the correct bias for a screening tool, but it is not a substitute for putting an instrument on the box.
going deeper — the full regulatory treatment, the measurement procedure, packing methods, labelling and documentation are in shipping magnetized material. Shielding design as an engineering problem — materials, saturation limits and containment — is covered in magnetic shielding & flux containment. If you have a shipment that has been refused, or a schedule that depends on air freight, talk to us before you book it — we ship magnetized product internationally every day and manage the shielding, packing and carrier arrangements that go with it.