Package size guide
Package size is the outer length, width, and height of what you drop off. Carriers do not care about the product’s listed inches. This guide helps you pick a container that fits — then you measure it for real.
Typical starting sizes (not a rate chart)
Common packs — measure your actual outer size before you buy postage
| Pack | Often used for | Watch for |
|---|---|---|
| 6×9 or 10×13 poly mailer | Clothes, soft goods | Overstuffing that balloons the height |
| #000–#2 bubble mailer | Small accessories | Items that puncture plastic |
| 6×4×4 to 8×6×4 box | Mugs, small kits | Still measure — brands vary |
| 12×9×6 or 12×12×6 box | Shoes, bundled goods | Empty space → DIM |
| 14×14×14 and up | Bulky gifts | Almost always check DIM |
How to choose
- Fit the item with just enough padding.
- Prefer a mailer when the item can flex.
- Prefer a box when it cannot.
- Measure the outside. How to measure a package.
- If the cube looks large and light, run DIM math, then compare rates.
Why “one size bigger” is expensive
An extra two inches on each side is not a rounding error. It is cubic volume. That is how a 1 lb gift becomes a 10 lb billable parcel. Right-size first; then chase cheap postage.
Collection-box limits
Blue USPS collection boxes reject parcels that are too thick or too long. A prepaid label does not override the slot. When in doubt, use a staffed counter or a UPS drop for boxed shipments.
Keep reading
Frequently asked questions
Measure it, then compare rates
Use the outer inches in Oshippy’s live USPS and UPS quotes.