The honest answer is that nobody can tell you a mailer size without knowing what goes in the parcel, and any site that hands you a chart is guessing. What we can do is narrow it fast by category, then give you one check that catches most mistakes.
Start from your category
| What you ship | Where to start | The trap |
|---|---|---|
| Folded apparel, one or two pieces | The folded garment footprint in the largest size you sell | Sizing to a medium, then finding a 2XL will not close |
| Books and print | The book laid flat, plus a small margin on each side | Depth. A single paperback needs far less than people order |
| Cosmetics or skincare sets | The tray or insert footprint, not the individual bottles | Bottle height, which sets depth and is measured capped |
| Mugs and ceramics | The cushioned unit, measured with the protection on | Corner protection on all six faces, not just the sides |
| Multi item kits | The packed stack, everything piled as it will sit | The card, sticker sheet and return slip nobody counted |
| Small electronics | The retail box, if it has one, plus cushioning | Loose cables that need their own space |
The one check that catches most errors
Pack a real order into whatever you have now, close it, then measure the parcel and calculate its dimensional weight: length x width x depth in inches, divided by 139 for typical US domestic retail rates. Compare that to the scale weight. If the dimensional weight is higher, you are paying to ship air and your next mailer should be shallower before it is anything else.
Run the same calculation on the mailer you are considering. If it drops you a billing band across your typical monthly volume, that difference usually dwarfs the unit price difference between two board grades.
Depth is where mailers go wrong
Length and width are usually obvious, because the product is flat on a table in front of you. Depth gets guessed, and guesses run high because people want to be safe. A safer approach is to build the packed stack physically, measure it with a ruler on the bench, and add a small allowance rather than a generous one. Void fill can take up slack, but it cannot take up a billing band.
Does the mailer need to be custom?
If your products vary enormously, a couple of sizes covering the spread is sensible. If you ship a consistent product, a mailer cut to it is better in every way, and at iBox the cutting die is included along with the plates, design support, US shipping and a digital proof, so a non round internal dimension costs nothing extra to tool. The only reason to round to a familiar number is if you are matching something else in your operation, such as an existing insert.
Ordering and lead time
Minimum order is 100 mailers, from about $0.48 per unit at bulk volumes, confirmed on your written quote. Turnaround runs in three lanes: rush (expedited production with air freight), standard (air) and cost saver (sea), from about 7 business days plus 2 to 5 for delivery, with specialty imported items up to about 12 weeks. Rush adds a premium of about 7 to 25% depending on the job. We produce in West Chicago and in Guangzhou.
For the full step by step method including board choice, see our guide to sizing a die cut mailer. To order, see mailer boxes.
Pack one real order, measure the parcel, and send those three numbers with your monthly volume when you request a quote. That is genuinely all we need to come back with a size and a price.
