Reference guide
How to Measure for a Mailer
Measuring for a mailer is not measuring a product. It is measuring what the product becomes once it has been folded, wrapped and packed with everything that travels alongside it.
This guide covers the three dimensions to take, how to take them on items that resist being measured, and why two suppliers quoting the same size can be describing different bags.
Taking the three measurements
Do this on a packed parcel, not on a product. Have the person who packs for you do the packing.
Pack a complete order
Product, card, tissue, returns slip, everything. Then fold it the way your team folds at working pace.
Measure the width at the widest point
Across the packed bundle, not across the flat item. Folds add width that flat measurements miss.
Measure the length at the longest point
Including anything that will not compress, such as a rigid box or a card that runs the full length.
Measure the depth under light pressure
Press down as a packer would while sealing, and measure there. Measuring an uncompressed lofty item overstates what you need.
Add an allowance for the closure
The contents must sit below the adhesive strip. Leave room for the flap to fold onto clean film.
Awkward products, and how to handle them
Five product types that resist straightforward measurement.
Lofty knitwear
Measure compressed rather than relaxed, but not squashed flat. Compressed under a hand is the realistic figure.
Irregular soft goods
Measure the smallest rectangle the packed item fits inside. That rectangle is what the bag has to accommodate.
Multiple items of different shapes
Pack them as they will actually be packed and measure the bundle. Measuring items individually and adding is always wrong.
Rigid boxes
Straightforward to measure and unforgiving in use. Size close, because a box that can move will damage its own corners.
Anything with a protruding part
A handle, a strap, a spout. Measure to the extremity, and consider whether it should be tucked or taped before packing.
Why suppliers quote sizes differently
Two identical numbers can describe different bags.
Some suppliers quote the usable area of the bag, with the closure flap sitting above it. Others quote the overall dimensions including the flap. The difference can be significant, and neither convention is wrong — they are just different.
There is a second variation: some quote nominal sizes rounded to a convenient figure, so a bag described as 12x15 and one described as 12x15.5 may be the same product from different suppliers.
The practical consequence is that comparing two numbers is not comparing two bags. Ask which measurement is being quoted, or better, compare physical samples — which takes ten minutes and removes the ambiguity entirely.
What to do with the numbers
Once you have three measurements for a packed parcel, you have what you need to choose a size and to check what a change would do to your shipping costs. Weigh the same parcel while you have it packed, because weight and depth together decide which pricing band it falls into, and a size change can move it in either direction. The sizes those measurements map onto are set out in the size reference table.
Questions about the measurement guide
Should I measure my product or my packed parcel?
The packed parcel, always. A flat garment measurement tells you almost nothing about what it becomes once folded with a card and a returns slip, and that folded bundle is what has to fit.
How do I measure something lofty like a knitted jumper?
Compress it under a hand the way a packer would while sealing, and measure there. Measuring it relaxed overstates the size you need; measuring it squashed flat understates it.
Do mailer sizes include the flap?
It depends on the supplier. Some quote the usable area with the flap above it, others quote overall dimensions. Ask which convention applies, or compare physical samples rather than numbers.