Yes, galvanized steel is magnetic. Galvanizing only adds a thin zinc coating to ordinary carbon steel, and the carbon steel underneath is strongly magnetic, so a magnet sticks to galvanized steel almost as firmly as it does to bare steel.
That simple fact is useful. It is how inspectors measure galvanizing thickness, it is the fastest way to tell galvanized steel from most stainless steel or aluminum, and it explains why a magnet test alone cannot always identify a metal. This guide covers all three.
Why Galvanized Steel Is Magnetic
Magnetism here comes from the iron in the steel. Galvanizing does not change the steel; it covers it. In hot-dip galvanizing, clean steel is lowered into molten zinc at about 850 F, where the zinc and iron react to form three zinc-iron alloy layers under a layer of pure zinc. The American Galvanizers Association gives a typical after-fabrication coating thickness of 3.0-6.0 mils (75-150 microns), and a much thinner coating on continuously galvanized sheet: G90 sheet carries 0.90 oz of zinc per square foot in total, or 0.45 oz per side (AGA Galvanized Steel FAQs, checked October 2026).
A few thousandths of an inch of zinc sits between the magnet and a beam, channel or sheet that may be anywhere from a fraction of an inch to over an inch thick. The magnet reaches straight through the coating to the steel. The coating does weaken the pull slightly, because it holds the magnet a tiny distance away from the steel, and that small effect turns out to be the basis of a standard test.
How Magnets Measure Galvanizing Thickness
Because zinc is non-magnetic and steel is magnetic, the strength of a magnet’s pull on galvanized steel drops as the coating gets thicker. Instruments use exactly that. ASTM E376 (checked October 2026) describes magnetic-type gauges that measure either the magnetic attraction between a magnet and the substrate or the reluctance of a magnetic flux path through the coating and substrate, and states that these gauges are designed to measure the thickness of a nonmagnetic coating on a magnetic substrate.
The AGA’s coating thickness guidance (checked October 2026) calls magnetic gauges a non-destructive, simple way to measure coating thickness and describes three types:
- Pencil-style gauges. Pocket-size, with a spring-loaded magnet. Accuracy depends on the inspector, so readings should be repeated.
- Banana gauges. Usable in any orientation without recalibration.
- Electronic gauges. The most accurate and easiest to use, and they can store and average readings.
This is why the magnetism matters on a steel job. Galvanizing on a beam, lintel or set of anchor bolts can be checked on site in seconds without damaging it. If the steel were not magnetic, inspectors would have to cut a sample for microscopy, which the AGA reserves for resolving disputes.
Magnet Test: Galvanized vs Stainless vs Aluminum
A magnet is the quickest field check for telling galvanized steel from look-alike metals. The table shows what to expect. Stainless grade behavior is taken from the Atlas Steels stainless steel grade datasheets, hosted by worldstainless (checked October 2026).
| Material | Magnet sticks? | Why |
|---|---|---|
| Hot-dip galvanized steel | Yes, strongly | Carbon steel core under a thin zinc coating |
| Galvanized sheet (G90 and similar) | Yes, strongly | Steel sheet with an even thinner coating |
| Bare or painted carbon steel | Yes, strongly | Ferromagnetic steel |
| Stainless 304 / 316, annealed | No | Austenitic structure; the datasheets describe both as non-magnetic |
| Stainless 301, cold worked | Yes | Cold work transforms part of the structure to martensite; the datasheet says these grades become strongly attracted to a magnet |
| Ferritic stainless (400-series type) | Yes | The datasheets state that all ferritic steels are readily attracted to a magnet |
| Aluminum | No | Not a ferromagnetic metal |
Where the magnet test misleads
A magnet that sticks proves the part contains magnetic steel. It does not prove the part is galvanized. Ferritic stainless steels are magnetic, and some austenitic grades pick up magnetism where they have been bent or drawn, because cold work changes their crystal structure. The opposite also happens: the same datasheets describe 302HQ as essentially non-responsive to a magnet even after substantial cold work. Use the magnet as a first sort, then confirm with the mill certificate, markings or the supplier. The way forming changes steel is covered in hot rolled vs cold rolled steel.
Other clues that a part is galvanized
- Finish. Hot-dip galvanizing is usually matte or bright gray, sometimes with a crystal spangle pattern, and dulls with age. Stainless keeps a brushed or polished look.
- Coating edges. Where galvanized steel has been cut or drilled after coating, the bare steel at the cut can show rust. Stainless shows the same metal right through.
- Thickness reading. A coating gauge shows a measurable coating on galvanized steel. On solid stainless there is no coating to measure.
For choosing between the two, rather than identifying them, see galvanized steel vs stainless steel.
Practical Uses of Galvanized Steel’s Magnetism
- Magnetic tools and fixtures. Magnetic levels, welding angle magnets and magnetic-base tools attach to galvanized beams and columns. Any coating or paint adds a gap that reduces holding force, so follow the tool maker’s guidance on coatings and minimum steel thickness, especially for magnetic drills.
- Magnetic signage and labels. Galvanized panels, doors and enclosures accept magnetic labels.
- Sorting scrap and offcuts. A magnet separates galvanized and carbon steel from aluminum and most 300-series stainless.
Magnetism has no effect on how galvanized steel welds, but the zinc coating does. Welding through it produces zinc fumes and burns away the protection; see can you weld galvanized steel for the safe way to do it.
Does Magnetism Affect Corrosion?
No. A part being magnetic tells you nothing about how well it resists rust. Galvanized steel resists corrosion because of its zinc coating, and once that zinc is consumed the steel underneath rusts like any carbon steel. How long the coating lasts, and what shortens it, is explained in does galvanized steel rust. Likewise, a stainless part that is slightly magnetic after forming is not necessarily a lower grade.
FAQ
Will a magnet stick to galvanized steel?
Yes. The zinc coating is thin and non-magnetic, and the carbon steel under it is magnetic, so a magnet grips through the coating.
Is zinc magnetic?
Not in any practical sense. That is why magnetic gauges, which ASTM E376 describes as measuring a nonmagnetic coating on a magnetic substrate, can measure galvanizing thickness.
Is galvanized steel more or less magnetic than regular steel?
The steel itself is unchanged. A magnet’s pull on the surface is slightly weaker because the coating holds it a little away from the steel, and the thicker the coating, the weaker the pull.
Can a magnet tell galvanized from stainless steel?
Usually, for common 304 and 316 stainless, which are non-magnetic when annealed. It cannot separate galvanized steel from ferritic stainless or from cold-worked austenitic stainless, which can both be magnetic.
Is galvanized pipe magnetic?
Yes. Galvanized pipe is zinc-coated steel pipe, so it is magnetic. Copper, brass, aluminum and plastic pipe are not.
Reference information only, not engineering advice. Disclaimer.