Poly Mailer Size Calculator
Enter a product’s length, width, and thickness to see the flat mailer size it needs and which common poly mailer sizes fit, with allowances you can adjust.
Poly Mailer Size Calculator calculates in your browser.
A mailer’s listed size isn’t the size of what fits in it
A 12 × 15.5 in poly mailer doesn’t hold a 12 × 15.5 in product. The film has to wrap around the item’s thickness, part of the length goes to the closure, and a snug item is hard to slide in. Sellers usually find this out by trial and error with a pack of the wrong size.
This calculator works out the flat size a product needs from its footprint and thickness, plus an ease allowance and a sealing allowance you can change. It then checks a documented set of common mailer sizes both ways round and picks the smallest that fits, with the room to spare on each side.
How to use the Poly Mailer Size Calculator
- Choose inches or centimeters.
- Enter the product’s length and width as it will lie in the mailer, folded or boxed if it ships that way.
- Enter its thickness at the thickest point.
- Adjust the ease and sealing allowances if your mailers or products need more or less room.
- Read the smallest listed size that fits, and check the table for the next size up.
How the calculation works
Needed width = product width + thickness + ease
Needed length = product length + thickness + ease + sealing allowance
Each size is checked with the long side along the mailer and turned across it
Recommended = the smallest listed size (by flat area) that fits
The listed sizes are 6 × 9, 7.5 × 10.5, 9 × 12, 10 × 13, 12 × 15.5, 14.5 × 19, 19 × 24, and 24 × 24 in, read as usable width × length excluding the flap. They are a reference set of widely sold sizes, not every mailer on the market.
| Product | Allowances | Minimum flat size | Smallest listed size |
|---|---|---|---|
| Folded T-shirt, 12 × 10 × 1 in | 0.5 in ease, 1 in seal | 11.5 × 14.5 in | 12 × 15.5 in |
| Paperback, 9 × 6 × 1.25 in | 0.5 in ease, 1 in seal | 7.75 × 11.75 in | 9 × 12 in |
| Hoodie, 35 × 28 × 5 cm | 1 cm ease, 2.5 cm seal | 34 × 43.5 cm | 36.8 × 48.3 cm (14.5 × 19 in) |
Calculated on your device
- The calculation runs in your browser as you type; nothing is sent to a server.
- Your sizes, weights, prices, and results are not sent to Looty Tools or stored.
- The calculator area is masked from session-recording analytics.
Limitations
- Recommendations are estimates, not guaranteed fits: soft products squash and stiff ones don’t, and film stretch varies.
- Mailer sizes differ by brand, and some quote the outside size or include the flap. Check the listed interior size.
- The flat-bag rule assumes a roughly rectangular product. Very thick or irregular items bulge, so the usable size is smaller than listed.
- It doesn’t judge protection. Fragile items usually need padding or a box.
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Guides
- Choosing a Poly Mailer SizeHow to size a poly mailer from a product’s length, width, and thickness, with worked examples for clothing and books and the common sizes they fit.
- 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.
Poly Mailer Size Calculator FAQ
- What size poly mailer does a folded T-shirt need?
- A shirt folded to 12 × 10 in and about 1 in thick needs at least 11.5 × 14.5 in flat with the default 0.5 in ease and 1 in sealing allowance, so the smallest common size that fits is 12 × 15.5 in. A 10 × 13 in mailer is too narrow.
- Why does the product’s thickness add to the width and the length?
- A flat mailer has to wrap around the product. Going around something W wide and T thick takes 2W + 2T of film, and a flat bag’s inside is half its perimeter, so the bag must be at least W + T wide — and L + T long — before any ease or sealing allowance.
- Are poly mailer sizes measured inside or outside?
- Sizes are given as width × length, and this calculator treats them as the usable area, excluding the flap. Some brands quote the outside size or include the flap, so compare the listed interior size of the mailer you buy.
- Can the product go in sideways?
- Yes. Each listed size is checked both ways round: with the product’s long side along the mailer’s length, and turned across it. The table marks a size that only fits turned as “Yes, turned”.
- When should I use a box instead of a poly mailer?
- When the product is thick — the calculator warns over about 3 in (7.62 cm) — rigid with sharp corners, or fragile. A flat mailer bulges around thick items, which makes its usable size smaller than listed, and it gives little crush protection.
- Are the sizes, weights, and prices I enter sent anywhere?
- No. The calculation runs in your browser as you type. Your sizes, weights, prices, and results are not sent to Looty Tools or stored, and the calculator area is masked from session-recording analytics. Refreshing the page clears it.
