US poly mailer size chart: how to pick the right size

How are poly mailer sizes measured?

US poly mailers are sold by width × length in inches. Width is the opening; length runs from the opening to the bottom seal. Both are the usable inside dimensions. The self-seal flap is not included, so a 10 x 13 in mailer has 10 by 13 inches of space plus a flap on top.

Because the factory side of the industry works in millimeters and microns, you will sometimes see the same mailer described as 254 × 330 mm. Our size and mil guide converts either way.

What is the standard US poly mailer size chart?

These are the sizes most US stores use, with typical contents. Treat them as starting points; how you fold and how thick the fabric is will move you one size up or down.

Size (W × L, in)	Millimeters	Typical contents
6 x 9	152 × 229	Jewelry, accessories, phone cases
7.5 x 10.5	191 × 267	Cosmetics, socks, small accessories
9 x 12	229 × 305	Documents, books, flat items
10 x 13	254 × 330	T-shirts, leggings, light tops
12 x 15.5	305 × 394	Hoodies, jeans, knitwear
14.5 x 19	368 × 483	Jackets, multi-item orders
19 x 24	483 × 610	Bulky apparel, coats
24 x 24	610 × 610	Bedding, pillows
28 x 40	711 × 1016	Comforters, large soft goods

Width × length, excluding the flap. Our standard range runs from 3 x 4 in to 31 x 43 in; other sizes are made on request.

How do you measure your product for a mailer?

1. Pack it as you ship it. Folded, in its inner polybag or tissue, with the packing slip.
2. Measure width, length and thickness of that packed item, in inches.
3. Minimum mailer width = product width + product thickness + about 1 in.
4. Minimum mailer length = product length + product thickness + about 1 in, so the flap closes flat without stretching.
5. Round up to the next size on the chart.
6. Test it. Seal the mailer and check the seams and corners. If the flap is under strain, go up a size; if the item slides around, go down one.

Example: a folded hoodie measures 11 × 13 in and is 2.5 in thick. Width: 11 + 2.5 + 1 = 14.5 in. Length: 13 + 2.5 + 1 = 16.5 in. A 12 x 15.5 in mailer is too tight; a 14.5 x 19 in mailer fits. If you would rather keep the smaller size, fold the hoodie differently and measure again.

Our poly mailer size finder does this calculation for you.

Why does a snug fit matter for shipping costs?

Carriers price the packed parcel, so an oversized mailer can cost you twice: extra film, and a bigger, puffier package.

• USPS flats. A flexible piece that is no more than 15 in long, 12 in high and 3/4 in thick, and uniformly thick to within 1/4 in, can be mailed as a flat (large envelope). Most filled apparel mailers are thicker than 3/4 in and pay parcel prices, but thin, flat items in a 9 x 12 in mailer may qualify.
• Parcel size limits. USPS caps parcels at 108 in in length plus girth (130 in for USPS Ground Advantage – Retail) and 70 lb. Poly mailers almost never get near these limits.
• Dimensional weight. Since July 12, 2026, USPS calculates DIM weight with a divisor of 139 for packages over one cubic foot (1,728 cubic inches), as UPS and FedEx do. A snug poly mailer usually keeps soft goods well under that volume, so you pay on actual weight. Our DIM weight calculator compares box and mailer side by side for UPS, FedEx and USPS.

How many sizes should you stock?

For most apparel and soft-goods stores, three sizes cover the large majority of orders, for example 10 x 13, 12 x 15.5 and 14.5 x 19 in. Each extra size splits your inventory and adds one more SKU that can run out in peak season. To choose, count last quarter's orders by product type and match each type to the smallest size that fits it.

What about thickness?

Size and thickness work together. A larger mailer holding a heavier order usually needs thicker film. As a rule of thumb, 2.5 mil (about 64 µm) suits most apparel, 2.0 mil suits light accessories, and 3.0–4.0 mil suits heavy or sharp-cornered items. The size and mil guide has the full table.

Getting the right sizes made

We manufacture poly mailers in our own factory in Istanbul, from film extrusion to printing and converting, and supply US businesses directly. Every size and thickness is made to order, so a mailer can match your best-seller exactly instead of the nearest catalog size. See our poly mailers page, or request a free sample kit to your US address and test the fit with your own products.

Sources

• USPS Domestic Mail Manual 101: Physical standards for letters, flats and parcels
• DCL Logistics: USPS DIM weight changes take effect July 12, 2026

General information based on published sources at the time of writing; not legal or tax advice. Carrier and marketplace rules change, check the current version.