Specification
Choosing a Poly Mailer Size
A size chart tells you what sizes exist. It does not tell you which one your product needs, because that depends on how your team folds, what goes in the parcel besides the product, and which shipping bands you buy on.
This page is the method. Work through it once and you will have a size mix that holds for years, rather than one you revisit every time a new product line launches.
Turn this into a specification
Tell us what you ship and we will apply everything on this page to your order, in writing.
The method
Half an hour once, rather than a recurring argument at the packing bench.
Pick your five most-shipped products
Not your whole catalogue. Five usually covers the large majority of your order volume, and they will cluster into two or three sizes.
Build a real order for each
Product, plus the card, the tissue, the sticker and the returns slip. Size against the parcel you actually send, not the item.
Have your own packers fold them
At working pace. A careful desk fold and a bench fold under pressure are different sizes, and you will get the second one.
Pack, seal and check the strip
The adhesive must meet clean film along its whole length. If contents reach the strip anywhere, the size is too tight.
Drop each parcel once from bench height
Flat, onto a hard floor. A seal that opens on one drop will open in a sorting hub.
Weigh and measure the packed parcels
Check them against the shipping bands you actually buy on. This is where a size decision quietly saves or costs real money.
Choose the smallest size that passes
If two sizes both work, the smaller one is cheaper per unit and travels better, because slack air makes a parcel less stable rather than more forgiving.
What to measure, and what not to bother with
Three measurements matter and one commonly quoted number does not.
Packed width
The widest point once folded, measured across the fold rather than across the flat item.
Packed length
The longest point once folded, including anything that will not compress.
Packed depth
The one most people skip, and the one that decides both fit and which shipping band you land in.
Flat dimensions of the product
Almost useless on their own. A flat garment tells you nothing about what it becomes when it is folded.
Common sizing mistakes and what they cost
These four account for most of the size decisions that get reversed within a year.
| Mistake | What it costs | Fix |
|---|---|---|
| Sizing against the product, not the order | A whole run that stops fitting once inserts are added | Pack a complete order before deciding |
| Choosing a tight size to save film | More in shipping than the film saved, because thickness rises | Weigh and measure the packed parcel |
| Buying one size larger for safety | Higher unit cost and less stable parcels | Choose the smallest that seals without strain |
| Standardising on one size across a varied range | Waste on light orders, failures on heavy ones | Two or three sizes, chosen from real order data |
When the answer is not a bigger bag
If parcels are arriving damaged rather than arriving burst, sizing up will not help — cushioning will, and more space can make things worse by letting contents move. Work out which failure you actually have before changing the size, because impact, abrasion, crushing and movement each need a different response. The diagnosis is set out in the protective mailer comparison, which starts from the damage rather than from the packaging.
Questions about size selection
How do I know what size poly mailer I need?
Pack a complete order — product, insert, tissue, returns slip — fold it the way your team folds at working pace, and pick the smallest size that seals onto clean film without strain. Ten minutes with two sample sizes settles it more reliably than any chart.
Should I size up to be safe?
No. An oversized mailer costs more per unit and leaves slack air, which lets contents move and makes damage more likely rather than less. The smallest size that closes properly is the right one.
How many sizes should I stock?
Two or three for most operations. One size means waste on small orders and strain on large ones; four or more introduces decisions at the bench that get made inconsistently once volume rises.
Do mailer dimensions include the flap?
Conventions vary between suppliers, which is why two identical-looking numbers can describe different bags. Rather than compare figures that may not mean the same thing, we confirm on each quotation which measurement applies.
Get a size recommendation
Tell us your five most-shipped products and roughly what goes in each parcel. We will recommend a size mix, explain the reasoning, and quote it.