Length x Width x Height: The Basics
Box dimensions are always listed in the same order: Length x Width x Height (or Depth). Length is the longest side of the opening. Width is the shorter side of the opening. Height is the distance from the opening to the bottom.
This sounds simple, but it trips people up constantly. A "12 x 10 x 8" box and a "10 x 12 x 8" box are the same box — just measured from different orientations.
Inner vs. Outer Dimensions
This distinction matters more than most people realize. Inner dimensions (ID) measure the usable space inside the box — what your product will fit into. Outer dimensions (OD) measure the outside of the box — what determines shipping costs and pallet configurations.
The difference is typically 0.5-1 inch per side, depending on the wall thickness. Always confirm whether a listed size is ID or OD before ordering. At Portland Boxes, we list inner dimensions unless noted otherwise.
The Goldilocks Rule
Your box should be 1-2 inches larger than your product in each dimension. This allows room for cushioning material (bubble wrap, foam, packing peanuts) without being so loose that the item shifts during transit.
Too tight: No room for cushioning. Product presses against walls and is vulnerable to puncture impacts.
Too loose: Item bounces around inside. Even with cushioning, excessive void space means wasted material, higher dimensional weight charges, and greater risk of shifting damage.
Just right: 1-2 inches of clearance on all sides. Snug enough to prevent shifting, roomy enough for protective cushioning.
Dimensional Weight
Carriers like UPS and FedEx charge based on the greater of actual weight or dimensional weight. Dimensional weight is calculated from the box size: (L x W x H) / a divisor (typically 139 for domestic, 166 for international).
This means an oversized box literally costs more to ship even if the product inside is light. Right-sizing your boxes can save 10-20% on shipping costs — which is why we stock over 200 sizes. There is almost certainly a box that fits your product better than whatever you are using now.