Packing Desk

Mailer sizing: outside size vs usable inside space

Updated Based on manufacturer documentation; not hands-on tested.

Mailer sizes are usually outside measurements. Seams, the closing flap, padding and the item's own thickness all eat into the space you can actually use.

Where the space goes

Outside size versus usable space in a padded mailer A mailer outline labeled outside size, with an inner dashed rectangle labeled usable space. The top strip is the flap and seal; the sides are seams and padding. flap and seal usable space minus item thickness seam + padding seam + padding outside size (e.g., 8.5 × 11.25 in)
Illustrative, not to scale. Usable space is smaller than the outside size because of seams, the flap, padding and the item's thickness.
  1. Side seams take a little from the width.
  2. The flap and seal take a strip from the length.
  3. Padding (bubble lining) takes more from both.
  4. Item thickness wraps around the edges: a 1 in thick item uses roughly 1 in of extra length and width to fit around.

Manufacturers usually list outside dimensions; for example, 3M lists the Scotch 8914 #2 plastic bubble mailer as 8.5 × 11.25 in. Inside dimensions are rarely published.

A simple estimating method (approximate)

For a padded mailer:

  • Usable width ≈ outside width − 1 in − item thickness
  • Usable length ≈ outside length − 2 in − item thickness

For an unpadded poly mailer, subtract about 0.5 in from the width and 1.5 in from the length (the flap), then subtract item thickness.

These allowances are rules of thumb, not manufacturer specs. Check with a sample mailer before buying in bulk.

Worked example: Scotch #2 padded mailer (8.5 × 11.25 in outside)

Item thicknessEstimated max item size
Flat (about 0.25 in)about 7.25 × 9 in
1 inabout 6.5 × 8.25 in
1.5 inabout 6 × 7.75 in

Cut-to-length wraps

Scotch Flex & Seal is sold in 15 in wide rolls. For an item L × W × H wrapped lengthwise, cut about 2 × (L + H) + 2 in, and check that W + H is under roughly 15 in. (Approximate; assumes the seal runs along one edge.)

Water-resistant isn't waterproof

Use the maker's words. 3M calls its plastic bubble mailers "moisture-resistant" and Flex & Seal "water and tear-resistant." Neither is a waterproof claim.

Leave room for the label

A 4 × 6 in shipping label needs a flat face at least that size. A #2 mailer (8.5 in wide) takes one comfortably.

Mailer options

Sources

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