Dimensions / Industrial & logistics / Poly mailers / Expandable mailer
An expandable poly mailer has a bottom gusset that opens for thicker items. Uline sells 10 × 13 × 2, 11 × 13 × 4, 13 × 16 × 4, 15 × 20 × 4, 20 × 24 × 4, 26 × 28 × 5 and 30 × 36 × 5 in (width × length × gusset) in 3 mil film; Interplas and Lavex use 2.5 mil. Sellers write the same bag in different orders: 15 × 20 × 4 at Uline, 15" x 20" + 4" at Interplas and 15" x 4" x 20" at Lavex. USPS measures pleated mailers like boxes, length × width × height ÷ 1728, not by length plus width.
| Uline S-11481: width × length × gusset | Uline S-13609: width × length × gusset | Film: Uline; Interplas, Lavex |
|---|---|---|
| 11 × 13 × 4in | 15 × 20 × 4in | 3mil2.5 mil |
Sources: Uline, Interplas. Checked October 2026.
Uline’s 11 × 13 × 4 in expansion mailer and a boxed item are filled in. Enter your mailer, its gusset and your item; each check follows a rule or figure on this page.
Enter the outside width × length with the flap left off, as US sellers list mailers; bubble mailers also carry a usable size on the maker’s sheet. The filled height below is the item’s thickness, plus 3/16 in of bubble lining on each side for a bubble mailer.
A 3.5 in thick item fits the 4 in gusset; 9 in wide fits the 11 in mailer, and 8 in long plus the gusset, 12 in, fits its 13 in. Our geometry: no maker publishes a rule.
Uline’s expansion mailer, 11 × 13 in with a 4 in gusset, is filled in. No maker publishes a sizing rule for gusseted mailers; this one is plain geometry.
Gusseted mailers are measured like boxes: 13 × 11 × 3.5 in, rounded down to the quarter inch, is 0.29 cubic feet, tier 0.3.
USPS sends pleated, expandable mailers to the box method: length × width × height, each rounded down to the quarter inch, divided by 1728.
Filled, the mailer is 13 × 11 × 3.5 in. UPS adds Additional Handling to soft packs over 18 × 14 × 6 in, FedEx over 18 × 13 × 5 in (longest side, second side, height): neither applies.
A filled gusseted mailer stands as tall as its contents. UPS measures bags at rest, with any tail taped down.
Selling expandable mailers? Photograph one opened out, mark its width, length and gusset in SizeMarker and send it with your quote.
Mark a photoSizes written the way each seller writes them; the gusset number moves.
| Seller and item | Size as written | Film; a case | Case weight |
|---|---|---|---|
| Uline S-17231With tear strip | 10 x 13 x 2" (outside W x L x D) | 3 mil; 100 | 4 lbs |
| Uline S-11481This page | 11 x 13 x 4" | 3 mil; 100 | 5 lbs |
| Uline S-11482 | 13 x 16 x 4" | 3 mil; 100 | 6 lbs |
| Uline S-13609 | 15 x 20 x 4" | 3 mil; 100 | 8 lbs |
| Uline S-15895 | 20 x 24 x 4" | 3 mil; 100 | 13 lbs |
| Uline S-13610 | 26 x 28 x 5" | 3 mil; 100 | 20 lbs |
| Uline S-15896 | 30 x 36 x 5" | 3 mil; 100 | 28 lbs |
| InterplasW x L + BG | 10" x 13" + 2"; 11" x 13" + 4"; 15" x 20" + 4"; 26" x 28" + 5" | 2.5 Mil; 1000, 500, 300, 100 | — |
| Lavex 422GM150420WebstaurantStore house brand | 15" x 4" x 20" | 2.5 mil; 300 | 16 lb shipping weight |
| Partners Brand EPM15204Staples | 15" x 20" x 4" | 100 | — |
Sources: Uline · Interplas · Lavex (WebstaurantStore) · Staples
| Item | What the sheet says |
|---|---|
| Gusset styleInterplas; Lavex; Staples | A bottom gusset that expands for bulkier items; Staples’ page says bottom in one line and sides in another |
| Order of the numbers | Uline width × length × depth; Interplas width × length + bottom gusset; Lavex width × gusset × length |
| UK notationPolybags | 15" x 18" + 3" is 15 in wide, 18 in long with a 3 in bottom gusset; a side gusset is written as x" wide opening to y" wide |
| FlapUline S-13609 | 2 in; post-consumer recycled content less than 5% |
| Gusset depths in stock | 2, 4 and 5 in (Uline, Interplas, Lavex) |
| Weight of one mailerOur division of the case weight, carton included | About 18 g (10 × 13 × 2 in) to 127 g (30 × 36 × 5 in) at Uline; about 24 g for Lavex’s 15 × 4 × 20 in |
| Capacity | No seller publishes a capacity in litres |
| Will it go inOur geometry | Thickness within the gusset, width within the mailer’s width, length plus gusset within its length: 11 × 13 × 4 in takes a 4 in thick item up to 11 in wide and 9 in long |
Sources: Interplas · Lavex (WebstaurantStore) · Staples · Uline · Polybags · Uline
| Rule | What it says |
|---|---|
| USPS: pleated mailersDMM 283.1.3.3 | Measured like a box: length, width and height at their largest, each rounded down to 1/4 in; length × width × height ÷ 1728 |
| Cubic limits from 12 July 2026 | Ground Advantage up to 1 cubic foot, Priority Mail up to 0.50 cubic foot; 20 lb and 22 in longest side |
| Priority Mail tiersMail Classification Schedule | Not over 0.1, 0.2, 0.3, 0.4 or 0.5 cubic feet |
| Ground Advantage tiersDMM 1.3.2 | Ten tiers in steps of 0.10, up to 1.00 cubic foot |
| Worked throughOur calculation | 13 × 11 × 3 1/2 in filled is 0.29 cubic feet, tier 0.3; 20 × 15 × 4 in is 0.69, Ground Advantage only |
| UPS: bagsRate and Service Guide | Measured with the exterior at rest; any tail compressed and taped to the body |
| UPS soft packsTariff of 17 April 2026 | Over 18 in long, 14 in on the second side or 6 in high: Additional Handling |
| FedEx soft packsService Guide 2026, US domestic | Over 18 in, 13 in or 5 in: Additional Handling; dimensional weight is L × W × H ÷ 139 |
Sources: USPS (Federal Register) · USPS (Federal Register) · Postal Regulatory Commission · UPS · UPS · FedEx
Uline’s run from 10 × 13 × 2 to 30 × 36 × 5 in, with 11 × 13 × 4, 13 × 16 × 4, 15 × 20 × 4, 20 × 24 × 4 and 26 × 28 × 5 in between. Interplas sells 10 × 13 + 2, 11 × 13 + 4, 15 × 20 + 4 and 26 × 28 + 5 in.
15 in wide, 20 in long, with a 4 in gusset. Check the order: Interplas writes the same bag 15" x 20" + 4", and Lavex 15" x 4" x 20", with the gusset in the middle.
Like a box: pleated mailers use length × width × height, each rounded down to 1/4 in, divided by 1728. Flat and bubble mailers are priced on length plus width instead.
3 mil at Uline, 2.5 mil at Interplas and Lavex.
If its thickness is within the gusset and its length plus the gusset fits the mailer’s length. An 11 × 13 × 4 in mailer takes a 4 in thick box up to 11 in wide and 9 in long.
Buyers ask how you write the size and which number is the gusset, whether the gusset is at the bottom or the sides, the film thickness, the flap and closure, the weight of one mailer and how many come in a case. Mark the real mailer opened out, with its gusset, on your own photo in SizeMarker, as in the picture at the top, and send one product card for WhatsApp or WeChat.
Working out the postage
Volumetric weight calculatorDimensional weight of a filled expandable mailer
