Shipping & packaging
What Size Poly Mailer Do I Need?
A poly mailer needs to be bigger than the product in a way that isn’t obvious from its listed size: the film wraps around the item’s thickness, the closure uses up length, and a product that only just fits is hard to slide in. Measuring three numbers and adding a few allowances gets you the right size before you buy a case of the wrong one.
Ready to try the tool this guide describes?
Measure the product the way it will ship
Fold or bag the item exactly as it will go out, then measure its length and width lying flat, and its thickness at the thickest point. A shirt folded in thirds is a different product, for mailer purposes, from the same shirt folded in quarters.
Measure soft items gently compressed but not squashed: the mailer won’t flatten them any more than your hand does.
Why thickness counts twice
A flat mailer is a tube of film sealed at both ends. To go around a product W wide and T thick, the film has to travel 2W + 2T. Laid flat, the bag’s inside width is half that loop, so it must be at least W + T. The same happens along the length.
So a 1 in thick item needs a mailer at least 1 in wider and 1 in longer than its footprint — before any room to slide it in.
Add ease and the closure
Ease is extra room so the product goes in without a fight; about 0.5 in (1 cm) is a reasonable start for flexible items, more for stiff ones. The sealing allowance is the length lost to the adhesive strip and the fold before the flap, often about 1 in (2.5 cm).
Needed width = width + thickness + ease. Needed length = length + thickness + ease + seal.
Worked examples
With 0.5 in of ease and a 1 in sealing allowance:
| Product as shipped | Needed flat size | Smallest common size |
|---|---|---|
| T-shirt, 12 × 10 × 1 in | 11.5 × 14.5 in | 12 × 15.5 in |
| Paperback, 9 × 6 × 1.25 in | 7.75 × 11.75 in | 9 × 12 in |
| Leggings, 10 × 8 × 1.5 in | 10 × 13 in | 10 × 13 in (no spare room) |
The leggings fit a 10 × 13 in mailer exactly, with nothing to spare. Going up to 12 × 15.5 in is the safer buy if the folds vary.
Checklist before you order
- Measure length, width, and thickness as packed.
- Add the thickness to both the width and the length.
- Add ease, and a sealing allowance to the length.
- Compare with the mailer’s listed interior size, not its outside size.
- Order a sample pack when a fit is within about a quarter inch.
Choosing a Poly Mailer Size FAQ
- Is a 10 × 13 poly mailer big enough for a T-shirt?
- Usually not for a shirt folded to 12 × 10 in and 1 in thick: it needs about 11.5 in of width with a little ease, and a 10 in mailer is too narrow. A 12 × 15.5 in mailer fits.
- Should I measure a folded item or an unfolded one?
- Measure it exactly as it will ship. Folding changes all three numbers, and thickness matters as much as the footprint.
- How much extra room should a poly mailer have?
- Add the product’s thickness to its width and length, then about 0.5 in of ease and about 1 in for the closure. Stiff products need more ease than soft ones.
- Can I put a product in a poly mailer sideways?
- Yes, if it fits that way. Turning the product means its long side runs across the mailer, which helps when the mailer is wide but short.
- Do poly mailer sizes include the flap?
- It depends on the brand. Many quote the usable area excluding the flap; some don’t. Check the listed interior dimensions before buying.
Related guides
- Poly Mailer Sizes ExplainedWhat the numbers on a poly mailer mean, how flaps and seams change usable space, and the largest flat item each common size holds at 1 inch thick.
- Poly Mailer vs BoxWhen a flat poly mailer stops being the right pack: thick, rigid, or fragile products, bulging, and the signs that a box or padded mailer is the better choice.
Open the tool
Jump into Poly Mailer Size Calculator when you are ready to process your files.
