Box measurements are always expressed in three dimensions

Length x Width x Depth

and always in that specific sequence.

The length and width are the opening dimensions of the box, and the length is always the larger of the two (unless they are equal). The depth is how far you can reach into the box, and is the distance measured perpendicular to the length and width. These measurements always relate to the inside dimensions of the box.

When measuring your box always leave space on all sides and above and below product for cushioning. such as bubble cushioning or loose fill.