Oct 13, 2026Buying Guides
How to measure the shipping bag size for my box?
Measure the box in three directions, then add allowances, because a bag has to wrap around the box's thickness.
Step 1: Measure the box
- Length (L): the longest side
- Width (W): the second longest side
- Height (H): how thick or tall the box is
Step 2: Calculate the minimum bag size
- Bag width = W + H (a flat bag has to stretch around the box's depth, so width alone isn't enough)
- Bag length = L + H + 2" (the extra 2" covers the flap and seal area)
Then add about 1" to the width for easy sliding and less strain on the seams.
Example
A box that is 10" × 6" × 3":
- Bag width: 6 + 3 = 9", plus 1" = about 10"
- Bag length: 10 + 3 + 2 = 15"
- Best fit: a 10" × 15" bag, or the next size up, like 12" × 15.5"
Tips
- Round up to the next standard size rather than down.
- Make sure the box fits with the bag sealed, not just inside it.
- For rigid boxes with sharp corners, go a little bigger or use a padded mailer so corners don't poke through.
- A box that's already thick (4" or more) often ships better in a cardboard shipper than a poly bag.
If you share your box dimensions, I can tell you the exact bag size to get.
