The honest answer is that the right size is the one that fits your busiest order profile with a little room to spare. Here is how to find it without buying five sizes and guessing.
Start from your order data, not from the product
Pull a month of shipped orders and sort by item count. Most stores find that a large share of orders are a single item, a smaller share are two or three items, and a thin tail is larger than that. You want a mailer that covers the first group comfortably and a second that covers the second group. The tail goes in a box or ships in two parcels, and it is not worth designing a mailer size around it.
A decision table
| What you ship | Start from roughly | Check |
|---|---|---|
| One folded t-shirt or similar soft item | A 9 x 12 in flat mailer | Does the seal close without pressing on the contents |
| A typical one to two garment apparel order | A 10 x 13 in flat mailer | Is there room for tissue and a card |
| Bulky knitwear, a hoodie, a folded jacket | A 14.5 x 19 in flat mailer | Does the pack thickness still leave sealing room |
| Multi item or bedding sized orders | A 19 x 24 in flat mailer | Would a box actually be cheaper on dimensional weight |
| Anything rigid or fragile | A box, not a mailer | Film resists water and abrasion, not crushing |
Those flat sizes are the ones the industry has converged on and they make a useful reference point. They are not our stock sizes, and because the tooling for a printed mailer is included in the job, a custom size costs no more than a familiar one.
Three mistakes that cost money
- Sizing to the average order. Every order above the average then needs a second size or a forced pack, and forced packs split.
- Forgetting the seal band. The adhesive strip and flap take roughly 2 in off the usable length. Contents pushed into that band is the most common failure.
- Ignoring thickness. A flat measurement works for paper. A one inch thick pack needs about an inch of extra width to wrap around it.
Weight and the carrier bill
A mailer is usually cheaper to ship than a box because it has almost no dimensional volume of its own, which matters when your carrier charges on dimensional weight. That advantage disappears the moment you oversize it, because a half empty mailer measures large and flops in a sorter. Get the size right and the mailer is the cheapest parcel you can send.
What you get when you print your own
Custom printed mailers start at a minimum of 100 units, with pricing from about $0.48 per unit at bulk volumes confirmed on your written quote. Design support, US shipping and a digital proof before anything prints are included. Turnaround is quoted per job in three lanes, rush (expedited production plus air freight), standard (air) and cost saver (sea), from about 7 business days, plus 2 to 5 for delivery.
Not sure which of two sizes to commit to, send us the measured packs and we will tell you which one your orders fit. Start at the quote form. For the full measuring method, read how to size a poly mailer, and for the alternative format see custom mailer boxes.
