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Poly Mailer Size Calculator

Estimate a flat mailer for one folded, soft item. See the target width and body length, then check a size you are considering.

Changing units converts measurements and allowances.

Enter decimal numbers without commas or units. Measurements: equivalent of 0.000001 to 1,000,000 cm. Allowances may be zero; blank allowances mean zero.

Folded item, including any inserts (in)
Sizing allowances · Uline guideline

Default total additions: 1.5 in (3.81 cm) to width and 3.5 in (8.89 cm) to length, after thickness. These follow the cited Uline guideline; change them for your supplier.

Blank allowances mean zero. These are total additions, not per-side amounts.

Reset clears item and candidate measurements; units and allowances are retained.

What size mailer should you look for?

Enter the folded item’s width, length, and thickness. The target size updates automatically.

A folded shirt can fit within a mailer’s flat outline and still leave too little room to close it. Thickness uses space across both flat dimensions. This tool adds thickness and adjustable allowances, then shows two ways to orient the item’s face.

How to measure before ordering

  1. Fold the item as it will ship. Include tissue, backing cards, and other inserts, and measure width, length, and thickness without assuming extra compression.
  2. Check the allowances against your supplier’s guide. The initial values follow the Uline product linked below, which lists outside flat dimensions excluding the flap.
  3. Compare available sizes with either target orientation. If checking a candidate, enter its opening width and body length using that same measurement convention, then test a sample.

Why thickness changes both dimensions

Target width = item width + thickness + total extra width.
Target body length = item length + thickness + total extra length.

The default total allowances are 1.5 inches for width and 3.5 inches for length, or exactly 3.81 cm and 8.89 cm. They are not per-side amounts. The cited Uline listing excludes its flap from the listed length; do not add that flap a second time to this guideline. Other suppliers may list inside dimensions, so obtain comparable measurements rather than assuming every listing uses the same convention.

Two worked examples

A folded item in inches

An item measures 8 × 11 × 1 inch (width × length × thickness). With the default allowances, target width is 8 + 1 + 1.5 = 10.5 inches. Body length is 11 + 1 + 3.5 = 15.5 inches. The target is 10.5 × 15.5 inches, excluding the flap.

A candidate that needs the other orientation

For that same item, turning its flat face gives a target of 11 + 1 + 1.5 = 13.5 inches wide and 8 + 1 + 3.5 = 12.5 inches long. A candidate 14 × 13 inch mailer meets this alternative guideline, although it is too short for the first orientation. A 10 × 17 inch mailer fails both orientations despite having more flat area than the first target.

What this estimate does not check

Seam construction, closure design, fabric bulk, film stretch, and folding variation affect physical fit. Use a product-specific guide for bubble mailers, rigid goods, fragile items, or gusseted bags. The tool does not determine protective packaging, mailability, or shipping rates. Custom allowances remain your assumptions.

Frequently asked questions

Are the extra allowances per side?
No. Each allowance is a total addition to one flat mailer dimension. The width calculation adds item width, thickness, and one total width allowance. The length calculation works the same way.
Does the target length include the sealing flap?
No. The target is the flat body length excluding the flap, following the cited Uline product’s convention. Do not add that product’s flap again to the default formula. If your supplier lists a different measurement, obtain the comparable body size before using this result.
Can I use it for bubble mailers or gusseted bags?
This version is for flat, unpadded, non-gusseted poly mailers. Lining, gussets, seam construction, and material stretch change the sizing method. Use your supplier’s guide for those products.
Why does turning the item change the target size?
The opening width and body length have different extra allowances. Turning only the item’s flat face swaps its width and length; thickness stays the same. The two results are alternatives, not two mailers to buy.
Does meeting the guideline guarantee a physical fit?
No. It means the candidate meets the entered dimensional allowance rule. Measure the folded item with inserts included and test a sample before ordering a batch.

Sources and sizing convention

The default formula follows the Uline poly mailer listing and sizing guide. Supplier conventions differ: EcoEnclose’s sizing guidance describes inside measurements and sample testing. Verify the exact product before ordering.

If your item needs a box

Use the Shipping Box Size Calculator to allow space around an item, or the Shipping Box Fit Calculator to check a box you already have.