How to measure a box
Box sizes are given as inside length × width × depth. Length is the longer side of the opening, width the shorter, and depth runs from the opening to the floor. Carriers, on the other hand, measure the outside.
Steps
- Open the box and look at the opening: the longer side is length, the shorter is width.
- Measure length and width inside, wall to wall, at the score lines.
- Measure depth from the floor to the top score line, not to the flap tips.
- Write them in the order length × width × depth.
- For shipping, measure the closed box outside, longest side first, and round as the carrier says.
Inside and outside differ
The walls add thickness. For a slotted box Packgent estimates the outside as inside plus two calipers on length and width and three on depth. The table shows the difference for a 12 × 10 × 8 in box.
| Board | Outside of a 12 × 10 × 8 in box |
|---|---|
| A flute | 12.38 × 10.38 × 8.56 |
| B flute | 12.25 × 10.25 × 8.38 |
| C flute | 12.31 × 10.31 × 8.47 |
| E flute | 12.13 × 10.13 × 8.19 |
| F flute | 12.06 × 10.06 × 8.09 |
| BC double wall | 12.56 × 10.56 × 8.84 |
| EB double wall | 12.38 × 10.38 × 8.56 |
| AC double wall | 12.69 × 10.69 × 9.03 |
Use it
- Inside outside dimensions
- Inside dimensions
- Outside dimensions
- Sizes
- Dimensional weight
- Right-sizing boxes to cut dimensional weight
- Reading a box maker's certificate
- Stacking strength and safety factors
Last reviewed 2026-10-27. Formulas and sources: method, sources.