Which Magnet Thickness Do You Actually Need? A Sizing Guide by Surface
By 360 Print Studio · September 22, 2026
The magnet that works on a fridge will not survive a highway. The one built for a car door is overkill for a mailer. Getting this right comes down to one decision: thickness. Custom magnets aren’t a single product, they’re three different materials, each built for a different job.
Which magnet thickness fits your surface?
The short answer: 14PT for anything that travels through the mail, 20mil for small shapes and indoor use, and 30mil for vehicle exteriors. Thickness controls three things — how rigid the piece is, how well it holds against wind and vibration, and whether it qualifies as mailable at all. Pick the surface first, then match the stock to it.
The short version
- 14PT promo magnets are thin enough to mail alongside a postcard campaign
- 20mil is the standard for die-cut shapes, fridge magnets, and indoor giveaways
- 30mil is the only thickness rated for full-time vehicle exterior use
- A 12x24 or 12x18 inch magnet on 30mil stock is the standard car door size
- Care habits matter more than magnet thickness for protecting paint
What is a 30 mil car magnet, and when do you need it?
A 30 mil car magnet is the heaviest-gauge magnetic stock we print, built specifically for vehicle doors and panels that sit outside in wind, rain, and temperature swings. Thinner material flexes and lifts at speed; 30mil stays flat against the panel and keeps its shape over months of daily driving. If you’re putting your business name on a van, truck, or sedan that’s actually on the road every day, this is the thickness to specify, printed full colour so your logo and contact details read clearly from the sidewalk.
Standard sizing for service vehicles is a pair of magnets, one per front door, most often 12x24 inches or 12x18 inches. That’s large enough to read at a stoplight but small enough to install and remove in seconds when the vehicle goes in for detailing or a wash.
The magnet that works on a fridge will not survive a highway.
Are car magnets safe for your vehicle’s paint?
Yes, with basic care. The risk isn’t the magnet itself, it’s what gets trapped underneath it: dirt, grit, or moisture that sits against the paint for weeks without air or light. Wipe the panel and the back of the magnet before installing it, and shift the magnet’s position every few days, especially if the vehicle sits in direct sun for long stretches. Vehicles wrapped in matte or textured finishes should skip magnets entirely, since the surface won’t hold a magnetic seal properly, but on a standard painted panel, a well-maintained 30mil magnet is a safe, fully reversible way to advertise a business.
WATCH OUT
Never leave a car magnet on the same spot for months without moving it. Trapped moisture is the actual cause of paint marks, not magnetic contact.
Can promotional magnets go through the mail as a mailer?
Yes, if they’re printed on 14PT stock, which is thin enough to mail alongside a postcard without triggering extra handling or weight issues. This is the piece that turns a mailer into something people keep. A postcard gets read once and often tossed; a magnet postcard gets read once and then stuck to a fridge or filing cabinet, where it keeps your name in front of the customer every time they walk past. If you’re already running a postcard drop for an appointment reminder, seasonal promotion, or new-customer offer, adding a 14PT magnet version to the mix gives the same message a much longer shelf life.
Which thickness works for a fridge magnet or countertop giveaway?
For a standard fridge magnet, 20mil is the right call — flexible enough to hold curved corners without cracking, rigid enough to sit flat on a metal door for years. This is also the thickness behind most die-cut shaped magnets, since it’s flexible enough to cut cleanly into a custom outline like a logo mark, a product silhouette, or a mascot, without the material splitting along the cut line the way a stiffer stock can. Keep the finished size at 3.5x2 inches or larger if you’re including a phone number, so the text stays readable at arm’s length.
What about die-cut shaped magnets for retail and packaging?
Die-cut-to-shape magnets on 20mil stock are the format to use when a plain rectangle undersells the brand. A bakery cutting a magnet in the shape of a cupcake, a landscaper cutting theirs into a leaf outline, or a retailer bundling a shaped magnet into a packaging insert are all using the die-cut step to make the piece feel designed rather than printed. The trade-off is a small increase in per-piece cost over a standard rectangle, since the custom shape requires its own cutting die, but that gap shrinks as the order quantity grows.
Business magnets: promo item, storefront signage, or vehicle ad?
The label “business magnets” covers three very different use cases, and each one points to a different thickness. A magnet meant to sit in someone’s home or office as a lasting reminder of your business — call it, gift shop, appointment card — belongs on 20mil. A magnet meant to travel through the mail as part of a marketing push belongs on 14PT. A magnet meant to ride on a vehicle every day belongs on 30mil. Mixing these up is the most common ordering mistake: a 20mil piece on a car door will curl and lift at speed, and a 30mil piece mailed as a promo item will blow past standard mailing weight.
| Thickness | Best for | Typical format |
|---|---|---|
| 14PT | Mailers paired with a postcard campaign | Standard postcard sizes, full colour |
| 20mil | Fridge magnets, die-cut shapes, retail giveaways | Custom shapes or small rectangles |
| 30mil | Vehicle doors and exterior panels | 12x24 or 12x18 inch rectangles |
How do custom magnets compare to a postcard mailer for follow-up?
A magnet and a postcard aren’t competitors, they’re a pair. The postcard delivers the message once and does the persuading; the magnet is what survives the desk drawer and keeps your name visible for the next six months. If you’re building a mail campaign around a seasonal push or a new-customer offer, pairing a postcard with a 14PT magnet insert gives the campaign both a short-term message and a long-term reminder in the same drop. Businesses running yard signs for the same campaign can find sizing guidance in our post on designing a yard sign a driver can read at 25 mph.
Where to start
If you’re outfitting a service vehicle, start with 30mil in a 12x24 or 12x18 inch size. If you’re building a mailer, go 14PT so it rides with a standard postcard. If you’re designing a giveaway, storefront magnet, or a shaped piece for packaging, 20mil is the stock to specify. Full colour is available across all three, so the decision is really just about where the magnet is going to live. Browse the full range and specs on our magnets page to get a proof started.
Photo by Yacine Ghozzia on Unsplash.
Frequently Asked Questions
What size car magnet do I need for a service vehicle?
Most service vehicles use two 12x24 inch or 12x18 inch magnets, one per front door, printed on 30mil stock. That thickness holds its shape at highway speed and resists curling in heat or cold better than thinner material.
Will a car magnet damage my paint?
Not if you follow basic care: keep the panel clean underneath, move the magnet every few days to let the paint breathe, and never leave it on for months in direct summer sun. Trapped moisture or grit under the magnet is what causes marks, not the magnet itself.
Can I mail a magnet like a postcard?
Yes, if it's printed on 14PT stock. That thickness is close to a standard postcard, which keeps it within normal mailing weight and lets it run through postal equipment without special handling.
What's the difference between 20mil and 30mil magnets?
20mil is a lighter, more flexible stock built for small die-cut shapes and indoor use, like fridge magnets or retail giveaways. 30mil is a rigid, heavier stock made for vehicle exteriors, where wind resistance and long-term shape retention matter.
Do die-cut magnets cost more than standard rectangles?
Die-cutting to a custom shape adds a tooling step, so shaped magnets typically run a bit more per piece than a plain rectangle at the same quantity. The gap narrows as order size goes up.
What's the minimum size for a fridge magnet with readable text?
Keep it at 3.5x2 inches or larger if you're including a phone number or address. Anything smaller forces type below a size most people can read at arm's length on a fridge door.