Mailer Size Calculator

Mailer width = Item width + Item height + Spare, Mailer length = Item depth + Item height + Spare + 4 — A mailer is a flat sleeve, so the item's thickness comes out of the width. The sleeve's circumference is 2 × its width, and the item needs 2 × (width + thickness), which means the mailer must be at least the item width plus one thickness. Add 2 cm to get the item in and out: a 25 cm wide item, 4 cm thick, wants a 31 cm mailer. The length works the same way, item length plus thickness plus ease, and then 4 cm for the adhesive lip, giving 40 cm — the lip folds over and no contents can sit in it. So the answer is "31 × 40 cm or bigger", and you buy the nearest stock size above it, say 32 × 45 cm. Measure compressible goods such as clothing at their squashed thickness. Watch how the supplier quotes sizes, too: some list the internal size, others the external size including the lip, and an external figure has to have the lip taken off before you compare.

With Item width 25cm, Item depth 30cm, Item height 4cm, Spare 2cm, the answer is Mailer width 31cm.

Enter Item width, Item depth, Item height, Spare. The result recalculates as you type, and an empty box counts as zero.

Changing only Item width (cm) moves the answer to Item width (cm) 12.5 → Mailer width (cm) 18.5 and Item width (cm) 50 → Mailer width (cm) 56. The table below lays out five steps.

Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.

Mailers do not cushion. Even a bubble-lined one only resists rubbing and pressure, so anything breakable belongs in a box. Skimp on ease and the contents ride up into the adhesive lip, the seal never bonds properly and the bag opens in transit — step up a size rather than trimming the allowance. Oversize is its own problem: the item slides about, corners get knocked, and the slack folds over the label where the scanner cannot read it. Forcing a thick item in stretches the film until it splits at a corner, so past about 5 cm of thickness use a box instead. Mailer size does help with volumetric weight, but price the freight against your own carrier's rules.