Most apparel brands can cover nearly their whole range with three or four poly mailer sizes. A typical set is 10×13 for single tops, 12×15.5 or 14.5×19 for hoodies and jeans, and one small and one extra-large size for the edges. Below is a size chart with what typically fits, a simple way to measure, what thickness and film to ask for, how USPS soft pack pricing ties into your choice, and how to plan your next order around peak season and Lunar New Year.
Poly mailer size chart
US mailer sizes are given as width x length in inches, measured flat, without the flap. Width always comes first. The usable inside space is a little smaller, because the side seals take up about a quarter to half an inch.
| Size (inches) | Size (cm) | Typical contents |
|---|---|---|
| 6 x 9 | 15 x 23 | Jewelry, phone cases, socks, small accessories, fabric samples |
| 7.5 x 10.5 | 19 x 27 | Baby onesies, ties, light cosmetics, a pair of socks or underwear |
| 9 x 12 | 23 x 30 | One folded T-shirt, leggings, scarves, paperbacks, flat prints |
| 10 x 13 | 25 x 33 | T-shirts, blouses, dresses, light knitwear, thicker books |
| 12 x 15.5 | 30 x 39 | Jeans, a light hoodie, skirts, flat shoes or sandals, two tees |
| 14.5 x 19 | 37 x 48 | Hoodies, jackets, jeans plus a top, boots, small throws |
| 19 x 24 | 48 x 61 | A full outfit, multi-item orders, twin bedding, light duvets |
| 24 x 24 | 61 x 61 | Puffer coats, comforters, cushions, large plush toys |
These are the sizes you find again and again on US supplier pages, but they are not a rule. Some brands use 9.5×12, 14×17 or 15×18 instead. We can make almost any size, so if your best-seller sits between two standard sizes, it can be worth having a mailer cut to fit it.
What about boxed shoes? A shoebox is rigid and thick, so it fills a flat mailer fast and leaves the corners under strain. Sandals, slippers and light sneakers without a box go fine in 12×15.5 or 14.5×19. Boxed shoes usually travel better in a carton.
How to measure your product
A flat mailer has no gusset. Every inch of product thickness takes space from both the width and the length. So the size that “looks right” on paper often turns out too tight.
- Fold the item the way you pack it. Measure it folded, not laid out.
- Measure width, length and thickness. Use the thickest point, like a hood or a zip.
- Add the thickness to both width and length. Then add about one inch for the side seals and easy loading.
- Leave room above the item for the flap to close flat. The flap should seal onto the bag, not press onto the product.
Example: a folded hoodie is 10 x 12 inches and 2 inches thick. You need about 13 inches wide and 15 inches long. A 10×13 will not close well. A 12×15.5 is snug. A 14.5×19 is comfortable. Order samples of two sizes and try them on your real stock before you commit.
Thickness and film
Most stock mailers in the US are 2 to 2.5 mil (about 50 to 63 microns). Custom printed mailers often run 2.5 to 3 mil. A mil is one thousandth of an inch.
- 2 mil is fine for single soft items in small and medium sizes.
- 2.5 mil is the common middle ground for apparel brands.
- 3 mil makes sense for heavy orders, sharp corners and the large sizes, where the bag carries more weight and gets dragged more on sorting belts.
For privacy, ask for co-extruded opaque film: white or a brand colour outside, grey or black inside. The dark inner layer stops anyone from reading what is in the parcel, even under strong light. We make poly mailer bags with a permanent adhesive strip in this kind of film, and can match the outside colour to a Pantone reference.
Reusable return mailers
If you sell apparel, you will get returns. A reusable mailer has two adhesive strips. The customer opens the parcel with a perforated tear strip, keeps the bag, and uses the second strip to send it back. No tape, no new bag, fewer “I didn’t have packaging” delays. The tear strip also opens cleanly, so the customer does not grab scissors and cut the bag, or the product.
Return mailers cost a little more per unit than single-use ones. Many brands use them only for the sizes and product lines with the highest return rates.
Shipping costs: why the size matters
Since 12 July 2026, USPS uses a dimensional weight divisor of 139 instead of 166, in line with UPS and FedEx. For USPS, dimensional weight applies to parcels over one cubic foot, which a filled mailer rarely reaches. UPS and FedEx apply it to all parcels, so a puffy, overfilled mailer can be billed at more than it weighs. Pack flat and squeeze out the air.
If you ship through a platform with USPS Ground Advantage or Priority Mail Cubic soft pack pricing, the price tier is set by the mailer’s length plus width, measured empty. In July 2026 USPS cut the soft pack tiers from ten to five, with the top tier ending at 36 inches. So a 9×12 (21 inches) sits in the lowest tier, a 10×13 in the second, and a 14.5×19 in the fourth. A 19×24 is outside cubic pricing. Moving a product down one size can lower the postage on every order. Check the current rules with your shipping platform before you change sizes.
Peak season planning
Black Friday is on 27 November and Cyber Monday on 30 November 2026. If you are reading this on the day we publish it, a new factory order will not arrive in time. For this peak, use your stock and local suppliers. Plan the next order now.
- Lead time. Our lead time is 4 to 6 weeks for a first order and 3 to 4 weeks for a repeat, plus sea freight to the US.
- Lunar New Year. Factories and forwarders across Asia slow down in early February 2027. See our Lunar New Year 2027 order deadline and confirm your Q1 restock before then.
- Count your January. Returns and post-holiday sales use mailers too. Many brands run short in January, not December.
- Book next year’s peak early. Printed mailers for Q4 2027 can be ordered in the summer, when lines are quieter.
Custom printed mailers
Printing turns a mailer into a small billboard on every doorstep. We print by gravure in up to 8 colours. On clear or dark film we lay down a white base layer first, so colours stay bright. Printing plates are kept for up to 2 years, so a repeat order does not need new plates unless you change the artwork. We can also use your own carton design, shipping marks and barcode labels, so goods go straight into your warehouse system.
Before you print, check three things with any supplier: the print area left after the flap and seals, where the shipping label will go so it does not cover the logo, and whether the ink rubs off on a sorting belt. Ask for a printed sample or a proof on the actual film.
Frequently asked questions
What is the most common poly mailer size?
10×13 inches is the most common size for US apparel brands. It fits one or two folded T-shirts, a blouse or a light dress. For hoodies and jeans, most brands move to 12×15.5 or 14.5×19.
Are poly mailer sizes measured inside or outside?
Sizes are the outside, flat dimensions without the flap, width first. The usable space is about a quarter to half an inch less on the width because of the side seals. Always add the thickness of your product to both width and length.
What thickness should a poly mailer be?
Most stock mailers are 2 to 2.5 mil. Choose 2.5 to 3 mil for heavier orders, items with corners and the large sizes.
Can you make a custom size?
Yes. We can make almost any size, with permanent or reusable tape, and in plain or printed film. Free samples of stock sizes are available so you can test fit before ordering.
Not sure which two or three sizes cover your range? Send us your product list or WhatsApp +84 898 545 893, and we will suggest sizes and send samples.
Sources: UPrinting poly mailer size guide; ValueMailers packaging size chart; eFulfillment Service guide to poly mailer sizes; Sticker Mule poly mailer specs; Pirate Ship, July 2026 USPS rate and rule changes; Federal Register, 31 March 2026.