How Fridge Magnets Work, and Which to Buy

By Fridge Magnets Editorial

A fridge magnet is a small ferrite or neodymium magnet sized to hold paper on a steel door. Flexible sheet holds 60 to 110 g and a 12 mm neodymium disc 2,500 g. A pressed photo magnet holds several times what sheet does, with no published figure. A painted door keeps roughly 70 percent of those figures.

Weigh what a fridge door is actually asked to carry. A takeaway menu is a few grams. A child's painting on thin card, a wedding invitation, a school calendar, a stack of twenty sheets of office paper that comes to roughly 100 g. Nothing on that list troubles a ferrite disc or a pressed photo magnet, and most of the disappointment people have with fridge magnets traces back to buying the one kind that holds 60.

That is the whole subject in one sentence, and the rest of this page is the detail behind it. Which magnet holds what, why the door changes the answer, how the pressed photo magnet on your parents' fridge is put together, and what to buy when you have a specific job in mind.

The five families

Almost everything sold as a fridge magnet belongs to one of five groups. Each has its own page in the types section, and the summary here is enough to tell them apart in a listing.

Flexible rubber sheet is ferrite powder mixed into vinyl and rolled flat, 0.5 to 0.75 mm thick for print work. It is the business card left by the plumber and the free calendar from the estate agent. Its surface field is about 300 Gauss, which is weak enough that you can bend the sheet double without it fighting you.

Pressed photo magnets put a print under a clear mylar cover in a crimped steel shell, with a flat ferrite magnet glued to the back. About 4 mm thick, hard-edged, and the type most people mean when they say photo magnet. Photo magnets covers the build and the ordering options.

Ceramic ferrite discs are the dark gray cylinders glued to the back of every souvenir sold at an airport. Grade C8 is the usual specification. Cheap, brittle, and happy up to about 250 C.

Neodymium is the modern alloy, NdFeB, normally sold in grade N42 for consumer parts. Nickel plated, chips when dropped on tile, and strong enough to change what a fridge door can be used for. A 10 mm cube holds 4,800 g.

Novelty magnets are the leftovers. Resin castings, laser cut wood and acrylic, letters for children, whiteboard clips. What holds them up is a ferrite or neodymium disc on the back, so their behavior is entirely the behavior of that disc. Judge a souvenir magnet by the disc, not by the paintwork.

Pull force for every common type

Pull force is the weight a magnet holds against gravity while pressed flat to steel. It is the only number worth comparing across types, and every figure below is a manufacturer value measured on a thick, flat, bare steel plate.

The pressed photo magnet has no row in that table because no seller publishes a pull force for one and nothing has been on a gauge here. The comparison we will stand behind is that a pressed magnet holds several times what a flexible sheet of the same footprint holds, which follows from the build. A rigid ferrite disc behind the steel shell carries far more magnetic material than 0.5 to 0.75 mm of ferrite powder mixed into vinyl. If a figure ever gets measured properly it will go in the table with the method beside it.

Two comparisons in that table are worth sitting with. At the same 50 mm footprint, a 20 x 3 mm neodymium disc holds about sixty times what a 0.5 mm sheet magnet holds. And a 6 mm neodymium disc, small enough to lose in a rug, out-pulls a ferrite disc more than three times its diameter. Size stopped predicting strength when neodymium arrived.

The sortable strength chart is the same data with a pounds column and a sort control. Magnet strength explained covers why Gauss readings mislead: a 12 mm N42 disc reads about 4,000 Gauss at the surface and a flexible sheet about 300, a ratio of thirteen, while the pull force ratio between them is far larger.

What the door does to those numbers

Every figure above assumes bare steel and full contact. A fridge door offers neither.

Paint adds 0.1 to 0.2 mm of gap between magnet and steel. That sounds like nothing. For a small disc, each tenth of a millimeter costs roughly 10 percent of the pull, because the field falls away fast over the first millimeter. Add a textured finish, add the gentle curve most doors have across their width, and the working figure lands at 60 to 80 percent of the plate value. Multiply by 0.7 and you will be close enough to buy on.

Run that against the table. A 20 x 3 mm ferrite disc at 500 g becomes about 350 g on a painted door. A 12 x 3 mm neodymium disc at 2,500 g becomes about 1,750 g. A 0.5 mm sheet magnet at 60 g becomes about 42 g, which is a takeaway menu and not much else.

Then there is the door that takes no magnets at all. Austenitic stainless steel, grade 304, is not magnetic. Its face-centered cubic structure, stabilized by nickel, holds no magnetic domain for a magnet to grip, and a lot of stainless fridge doors are made of it. Ferritic stainless, grade 430, is magnetic, which is why one stainless fridge in a showroom takes magnets and the one beside it does not. The side panels are the usual escape route, since most models use painted mild steel there and it is magnetic even when the door is not. Why magnets do not stick to stainless has the full picture, including the tricks that work on 304.

How a magnet holds on at all

A magnet on a door is completing a circuit. Field leaves one pole, passes into the steel, travels through it, and returns to the other pole. Steel carries that field far more readily than air does, so the magnet is pulled towards the arrangement with the most steel and the least air in the path. Contact area matters, gap matters more, and the mass of the magnet itself is almost irrelevant to how well it holds.

Which explains a common complaint. A heavy resin souvenir with a 20 mm ferrite disc slides down a textured door, while a thin pressed magnet on the same door does not move. The souvenir's disc sits proud of an uneven back, holding maybe half its face against the paint, and it is carrying its own weight as well as the postcard. How fridge magnets work goes through the flux path properly, and the rest of the science section covers what happens at the door surface.

Inside a pressed photo magnet

Four layers, front to back. A clear mylar cover, which is the shiny face you touch. The photo print itself. A steel shell whose rim the press crimps over the edge of the mylar, locking the sandwich shut. A flat ferrite magnet glued to the back of the shell. Overall thickness comes to about 4 mm.

The crimped rim is doing more work than it looks. It seals the print edge, so humidity above a kettle does not lift the corner, and it gives the magnet a hard perimeter that survives being knocked off a door onto a tile floor. That is the practical difference between a pressed magnet and a laminated sheet print of the same picture: one has a steel edge, the other has an exposed paper edge.

The magnet on the back is ferrite rather than neodymium, and deliberately so. Ferrite is cheap, flat, and in this format holds far more than any photo magnet will ever be asked to carry. Neodymium in the same footprint would cost more and hold multiples of what the job needs. How photo magnets are made follows the production sequence, and magnetic sheet versus pressed compares the two builds side by side.

Flexible sheet, and where it earns its place

Flexible sheet gets a bad write-up on this site because it is usually sold for jobs it cannot do. Sixty grams at 0.5 mm is a weak magnet by any measure.

It has three genuine advantages though. It can be die cut into any outline, including shapes with holes in them, which no pressed format allows. It costs a fraction of a pressed magnet per unit, and it ships flat and light. And it can be printed as one large sheet then cut, which is why promotional runs use it almost exclusively.

Buy 0.75 mm rather than 0.5 mm when the choice exists. The jump from 60 g to 110 g is the largest proportional gain available anywhere in the flexible range, and the sheet is still thin enough to cut with scissors. Flexible rubber magnets covers grades and print surfaces.

The hard novelty types

Resin, wood, acrylic, and molded plastic magnets all work the same way. A body carries the artwork, a disc on the back carries the load, and the two are held together with glue.

Cast resin gives depth to a picture, which is why so many tourist magnets use it. The failure point is the glue joint rather than the magnet: a resin body of any size levers on that joint every time someone knocks it, and a 20 mm ferrite disc left on the door with the souvenir in your hand is the usual result. 3D resin magnets covers what to check.

Laser cut wood and acrylic sit flat and thin, so they stay put better than resin, and the artwork is either engraved or printed on the face. Wood and acrylic magnets has the material differences.

Office and whiteboard magnets are a different job entirely. A whiteboard is thin steel with an enamel or laminate coating, which behaves like a painted fridge door, and the magnets sold for it are usually neodymium in a plastic cup so nothing scratches the writing surface. A 10 mm N42 cube at 4,800 g will hold a stack of paper on a whiteboard that a ferrite button would drop. Whiteboard and office magnets and office ideas go further.

Promotional magnets are their own category because the buying decision is different. Nobody orders 500 of anything for its holding power. Promotional and business magnets covers the formats printers actually stock, and decorative and art magnets covers the other end, where the magnet is the object rather than the fixing.

Ferrite against neodymium

At the same 20 x 3 mm size, ferrite holds 500 g and N42 neodymium holds 3,500 g. Seven times, from a magnet that looks identical across a table.

Ferrite wins on price, on heat, and on not caring what happens to it. Its maximum working temperature is about 250 C, so a ferrite magnet on a fridge in a hot kitchen or in a car in summer is in no danger. It is brittle and will crack if you drop it on tile, but a cracked ferrite disc still works.

Neodymium wins on strength and on nothing else. Its working temperature tops out at about 80 C, which is fine on a fridge and not fine on a radiator or a dashboard. The nickel plating chips when two of them snap together, and once the plating is broken the core corrodes. It loses roughly 1 percent of its strength per decade at room temperature, which is slow enough that it will outlast the fridge. Neodymium versus ferrite sets the two out in full, and how long magnets last covers the decay figures.

The safety picture belongs here rather than in a box at the bottom. Small neodymium magnets are the reason magnet safety warnings exist at all. Two of them swallowed separately can attract through the wall of the gut and pinch the tissue between them, which is a surgical emergency, and the CPSC keeps a safety center on exactly this. That risk is specific to small, strong, loose magnets. It is not a reason to avoid a 57 mm photo magnet, which no child is swallowing, and it is a very good reason to keep 6 mm discs off a fridge in a house with a toddler. Letter and number sets for children use large molded bodies with the magnet buried inside for the same reason. Kids' letter and number magnets covers what to look for.

Two smaller cautions. Neodymium near a bank card is a real effect on old magnetic stripes and irrelevant to a chip, which magnets and credit cards explains. And heat above 80 C permanently weakens N42, covered in magnets in heat.

Sizes, and how many fit a door

Usable door width on most models runs 40 to 60 cm. The arithmetic from there is simple and worth doing before you order thirty of something. At 57 mm plus roughly 10 mm of breathing space, a 50 cm door takes seven across. At 102 mm, the same door takes four. Vertically you have most of the door height, but the top third is where people actually look, so plan for four or five useful rows rather than the full stack.

Shape interacts with crop more than buyers expect. A round magnet at 57 mm shows less of a photograph than a 64 mm square does, and it crops faces at the edge of a group shot. Square is the safer default for people, round for a single subject with space around it. The size visualizer draws each of these at true scale on screen so you can hold a bank card against it, and sizes and thickness has the ordering detail.

How the picture gets on

Three routes, in rough order of how they feel in the hand.

A pressed magnet takes a printed paper insert, cut to size, and traps it under mylar. Print quality is whatever the printer's paper and press deliver, and the mylar adds gloss.

A flexible sheet magnet is either printed directly on a white-coated magnetic face or laminated with a separate printed sheet. Direct printing is cheaper and thinner, lamination protects the ink.

A hard novelty magnet carries the image as a printed insert under resin or epoxy, or as artwork printed straight onto wood or acrylic. Printing methods goes through each of these and what to ask a supplier for. We have not run fade testing on any of them, so treat longevity claims in a product listing as the seller's claim rather than a measurement.

What to buy for each job

For photographs, the choice between builds is decided by the edge. Buy pressed if the magnet will be handled, moved between doors, or given as a gift. Best photo magnets ranks what is available, and the reviews section has a ranking for each of the categories in the table.

For paper, resist the urge to buy the biggest disc on the page. A 20 x 3 mm N42 disc holding 3,500 g will hold your electricity bill, and it will also take a fingernail to lift off a smooth door. A 10 x 2 mm disc at 1,400 g is easier to live with.

For a promotional run, the calculation is per unit rather than per magnet. Sheet magnets are listed at $1.20 each from Vistaprint with a minimum order of 25, and at $2.50 each from Shutterfly with a minimum order of 1. Those two listings bracket most of the market, and price per magnet works through the total including setup and shipping. How many to order covers the quantity question, and the buying section holds the rest of the ordering advice.

Reading a seller's listing

A good listing states the material, the size in millimeters, and the thickness. A vague one gives you a picture and an adjective.

Look for the magnet type by name. Ferrite, neodymium with a grade, or flexible vinyl. A listing that says only "strong magnet" is describing a feeling. Look for thickness in millimeters, since 0.5 and 0.75 mm sheet magnets look identical in a photograph and differ by nearly double in holding power. Look for a pull force figure with a unit, and assume it was measured on bare steel.

Treat missing numbers as missing rather than as bad. Plenty of reputable sellers do not publish price per magnet, thickness, or minimum order, and the honest thing to say about those is that they are not published. What to look for is the longer checklist, and our editorial policy explains why this site refuses to fill blanks with estimates.

Check the return position on custom print work before you order. A custom magnet with your photograph on it cannot be resold, and sellers differ on whether a print error is theirs or yours.

Care, cleaning, and storage

Wipe the door and the magnet face before placing anything. Grit trapped under a magnet is what scratches paint, and a magnet that has lived in a drawer has collected steel dust that you cannot see. This is the only real answer to whether magnets damage fridges: the magnet does not, and the grit under it might.

Slide magnets off rather than pulling straight out, and slide them onto the door rather than letting them snap on. Ferrite chips at the rim when it lands hard, and a nickel-plated neodymium disc that snaps flat against steel takes a bright mark where the plating flattened.

Store spare neodymium with a spacer between the discs, or with a steel keeper across the poles, and keep the stack away from anything with a magnetic stripe. Ferrite and pressed magnets need nothing special, though a box of pressed magnets face to face will scuff the mylar. How to store magnets has the detail.

If a magnet has stopped holding, the magnet is rarely the problem. Check for a sticker or a felt pad added to the back, check whether the door has been repainted, and check whether the magnet is sitting on a curve where only its edge touches. Real magnetic decay in ferrite or neodymium runs at about 1 percent per decade, which is not what changed in the eighteen months since you bought it.