How to Measure Room
How to Measure

How to Measure a Box for Shipping

Measure length, width, and height at the longest point of each side, in inches, and round up to the next whole inch. Carriers use these three numbers to calculate dimensional weight, which can cost more than the box's actual weight.

Measure a box’s length, width, and height in inches, each at the longest point of that side, and round up to the next whole inch. Carriers use these three numbers — combined with the box’s actual weight — to calculate what they’ll charge, and for an oversized or lightweight box, that charge can be based on size rather than weight.

Measuring the box

  1. Length: the longest side of the box’s base.
  2. Width: the shorter side of the base, perpendicular to length.
  3. Height: the vertical dimension, from the base to the top.

Measure the outside of the box (not the inside usable space), and round each measurement up to the next whole inch — carriers generally round up too, so measuring precisely to a fraction of an inch doesn’t gain you anything.

Understanding dimensional weight

Shipping carriers charge based on whichever is greater: the box’s actual weight, or its dimensional (DIM) weight — a calculated weight based on the box’s volume. This exists because a large, lightweight box takes up truck or plane space out of proportion to its actual weight.

The formula:

Length × Width × Height (inches) ÷ DIM divisor = DIM weight (lbs)

The DIM divisor varies by carrier and service level — 139 is common for US domestic ground shipments, though it’s worth checking your specific carrier’s current published divisor, since these do change.

Example: an 18” × 14” × 12” box → 18 × 14 × 12 = 3,024 ÷ 139 ≈ 21.8 lbs DIM weight, rounded up to 22 lbs. If the box’s actual contents weigh only 8 lbs, the carrier would charge based on the 22 lb DIM weight instead.

Choosing a box size for an irregular item

For an item that isn’t already box-shaped, measure its longest point in each of the three dimensions, then choose a box sized at least that large in every direction, plus 1-2 inches of extra space per side for padding material (bubble wrap, packing paper, or air pillows) between the item and the box walls.

A quick way to keep shipping costs down

Since DIM weight is based on volume, the single biggest lever for keeping shipping costs low on a lightweight item is choosing the smallest box that reasonably fits it — an oversized box with excess empty space increases the DIM weight charge without adding any real protection beyond what proper padding already provides.

Frequently Asked Questions

What order do you measure a box's dimensions in?

Length, width, then height is the standard order most carriers expect: length is the longest side of the base, width is the shorter side of the base, and height is the vertical dimension. Getting the order right matters when you're entering dimensions into a shipping calculator, since some tools calculate differently if the numbers are out of order.

What is dimensional weight and why does it matter for shipping?

Dimensional (DIM) weight is a calculated weight based on a box's volume, not its actual weight — carriers charge based on whichever is higher, DIM weight or actual weight. A large, lightweight box (like one full of pillows) can cost more to ship than its actual weight would suggest, because its DIM weight is higher.

How do you calculate dimensional weight?

Multiply length x width x height (in inches) to get the volume, then divide by a carrier-specific DIM divisor (commonly 139 for domestic US shipments, though it varies by carrier and service level). The result, rounded up, is the DIM weight in pounds — compare it to the actual weight, and the carrier charges based on whichever is higher.

Do you measure a box's inside or outside dimensions for shipping?

Outside dimensions — carriers charge and size-restrict based on the box's exterior measurements, since that's what determines how much space it takes up in a truck or plane, regardless of how much room is actually usable inside.

How do you measure an irregularly shaped item for a box?

Measure the item at its longest point in each of the three dimensions (length, width, height), then choose a box at least that large in every direction, plus a couple inches of padding space on each side for cushioning material.

← Back to How to Measure