Dimensions / Industrial & logistics / Poly mailers / Flat poly mailer
A flat poly mailer is sized by its outside width × length, flap left off: Uline lists 6 × 9, 7 1/2 × 10 1/2, 9 × 12, 10 × 13, 12 × 15 1/2, 14 1/2 × 19, 19 × 24 and 24 × 24 in, with a 2 in flap on top, and IPG’s Fastpak comes in the same sizes. The film is 2.5 mil (EcoEnclose) or 3 mil (Uline) in the US; British and German makers give microns, 45 µm (Polybags) to 70 µm (VP), and the inside size. Uline sizes a mailer as width + thickness + 1 1/2 in by length + thickness + 3 1/2 in, and USPS prices it on length plus width: a 10 × 13 in mailer makes 23 in, cubic tier 0.2.
| A common size, Uline S-3354: outside W × L, flap left off | Film: Uline; EcoEnclose | Uline’s sizing rule: item width + thickness +; length + thickness + |
|---|---|---|
| 10 × 13in | 3mil2.5 mil | 1 1/2in3 1/2 in |
Sources: Uline. Checked October 2026.
Uline’s 10 × 13 in mailer and a folded shirt are filled in. Enter your mailer 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.
Uline’s rule: width + thickness + 1 1/2 in is 9.5 in, within the 10 in mailer; length + thickness + 3 1/2 in is 12.5 in, within its 13 in.
Uline’s 10 × 13 in tear-proof mailer and a folded shirt of 7 × 8 × 1 in are filled in. The rule is Uline’s own sizing advice, and its chart leaves off the 2 in flap.
Length 13 in plus width 10 in, each rounded down to the quarter inch, make 23 in: tier 0.2 for Ground Advantage and Priority Mail soft packs.
USPS cut soft-pack cubic pricing to five tiers on 12 July 2026, the same for Ground Advantage and Priority Mail; a 10 × 13 in mailer adds up to 23 in.
Filled, the mailer is 13 × 10 × 1 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 flat mailer is about as thick as what is inside. The FedEx limits cover US domestic shipments only.
Selling poly mailers? Photograph one, mark its width, length and flap in SizeMarker and send it with your quote.
Mark a photoOutside width × length in inches, flap left off. Case counts and weights as each seller prints them.
| Size (in) | Uline: a case; lbs a case | IPG Fastpak: a case | EcoEnclose 2.5 mil: one mailer |
|---|---|---|---|
| 6 × 9 | S-17229, with tear strip: 1,000; 14 | 1000 | 0.013 lb (0.2 oz) |
| 7 1/2 × 10 1/2 | S-20785: 1,000; 21 | 1000 (7.5 × 10.5) | — |
| 9 × 12 | S-13608: 1,000; 28 | 500 | — |
| 10 × 13This page | S-12908: 1,000; 34 | 500 | 0.028 lb (0.4 oz) |
| 12 × 15 1/2 | S-12909: 500; 24 | 500 (12 × 15.5) | 0.036 lb (0.6 oz) |
| 14 × 17 | S-17230: 500; 30 | — | — |
| 14 1/2 × 19 | S-21873: 500; 33 | 250 (14.5 × 19) | 0.0552 lb (0.8 oz) |
| 19 × 24 | S-21874: 250; 26 | 125 | 0.092 lb (1.4 oz) |
| 24 × 24 | S-21875: 200; 36 | 125 | — |
| 24 × 36 | S-21876: 200; 41 | — | — |
Sources: Uline · IPG · EcoEnclose
| Maker | What the sheet says |
|---|---|
| Uline, USTear-proof line | 3 mil, three-layer co-extruded polyethylene, RIC #4; sizes are outside W × L and leave off the 2 in flap; post-consumer recycled content less than 5% |
| EcoEnclose, US | 2.5 mil; 100% recycled LDPE, 56% post-consumer and 44% post-industrial; made in USA |
| IPG Fastpak | 100% polyethylene with a silver/gray inner layer for privacy; no thickness published |
| Polybags, UKInside sizes | 165 × 230 mm and 216 × 356 mm at 45 µm, 305 × 406 mm at 50 µm; 100% recycled grey 250 × 350 mm at 55 µm |
| VP docuCARE classic, GermanyExternal = internal + flap | 165x220+40, 250x350+40 and 320x420+40 mm at 70 µm; white outside, black inside |
| Gauge and milPolybags; our conversion | 100 gauge = 1/1000 of an inch and 400 gauge = 100 micron, so 1 mil = 25.4 µm |
| Which side is the widthPolybags | The width is always the side that opens |
Sources: Uline · EcoEnclose · IPG · Polybags · VP Group · Polybags
| Rule | What it says |
|---|---|
| Uline’s sizing ruleS-3354 page | Width of product + thickness + 1 1/2 in; length of product + thickness + 3 1/2 in |
| Worked throughOur calculation | An item of 7 × 8 × 1 in needs 9 1/2 × 12 1/2 in: the 10 × 13 in mailer |
| USPS soft-pack cubicDMM 283.1.3; tiers from 12 July 2026 | Outside length + width, each rounded down to 1/4 in: up to 21 in tier 0.1, 27 in 0.2, 31 in 0.3, 34 in 0.4, 36 in 0.5; longest side 22 in, 20 lb |
| Tiers by sizeOur calculation | 6 × 9 → 15 in, 0.1; 10 × 13 → 23 in, 0.2; 12 × 15 1/2 → 27 1/2 in, 0.3; 14 1/2 × 19 → 33 1/2 in, 0.4; 19 × 24 → 43 in, no cubic price |
| USPS large envelope (flat)Mail Classification Schedule 1115.1 | Up to 15 × 12 × 0.75 in and 13 oz; a piece that is rigid or not uniformly thick pays the package price |
| UPS and FedEx soft packsUPS tariff 2026; FedEx Service Guide 2026 | Additional Handling over 18 in long, 14 in (UPS) or 13 in (FedEx) on the second side, or 6 in (UPS) or 5 in (FedEx) high |
| Royal Mail Large LetterRoyal Mail Wholesale | 353 × 250 × 25 mm and 750 g, overhanging polythene included, corners pulled out before measuring |
| UK Plastic Packaging TaxHMRC | Below 30% recycled plastic: £228.82 a tonne from 1 April 2026, for businesses with 10 tonnes or more in 12 months |
| EU PPWRRegulation (EU) 2025/40, Articles 7 and 24 | 35% post-consumer recycled plastic from 2030; e-commerce packaging at most 50% empty space |
Sources: Uline · USPS (Federal Register) · USPS (Federal Register) · Postal Regulatory Commission · UPS · FedEx · Royal Mail Wholesale · Royal Mail Wholesale · HMRC (gov.uk) · EU PPWR
Uline and IPG’s Fastpak both sell 6 × 9, 7 1/2 × 10 1/2, 9 × 12, 10 × 13, 12 × 15 1/2, 14 1/2 × 19, 19 × 24 and 24 × 24 in; Uline adds 14 × 17 and 24 × 36 in. Each is the outside width × length without the flap.
In the US it is the outside width × length with the flap left off: Uline’s chart says so and gives the flap as 2 in. British and German makers list the inside size instead: Polybags prints “internal size”, and VP adds a 40 mm flap to the size it gives.
2.5 mil at EcoEnclose and 3 mil for Uline’s tear-proof line. European bags are given in microns, from 45 µm (Polybags) to 70 µm (VP); 1 mil is 25.4 µm.
Uline’s rule: width of the item + thickness + 1 1/2 in, and length + thickness + 3 1/2 in. An item of 7 × 8 × 1 in needs 9 1/2 × 12 1/2 in, so a 10 × 13 in mailer.
EcoEnclose gives 0.028 lb (0.4 oz) for a 2.5 mil 10 × 13 in mailer and 0.092 lb (1.4 oz) for 19 × 24 in; a case of 1,000 of Uline’s 3 mil 10 × 13 in mailers weighs 34 lbs.
Buyers ask for the outside width and length and whether they include the flap, the film in mil or microns and how many layers, the colour inside and out, the recycled share, the seal and tear strips, the weight of one mailer and how many come in a case. Mark the real mailer 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 flat mailer
