by Heeva Asefvaziri, CPP April 14, 2021 4 min read

Correct box dimension measurements play a critical role in the calculation of shipping costs for your e-commerce store. They will impact your total shipping cost regardless of whether you choose to ship via UPS, USPS, or FedEx. In this article, we’ll discuss:

  1. How to measure the outside dimensions of a box
  2. How to calculate a box's volume
  3. How to determine a box’s dimensional weight
  4. How to arrive at a proper calculation for your shipment by determining it’s billable weight

What Are Outside Dimensions?

The outside dimensions of a box are the measured length, width, and height of an assembled box. They are determined once a box has been completely assembled and taped closed. They are usually not the same as inside dimensions since inside dimensions do not take into account the material thickness of a shipping box.

How To Measure A Box’s Outside Dimensions

First, be sure to use a good quality, well marked tape measure. For the last 10 years, my personal favorite tape measure has been the Stanley 16 ft. Powerlock. It’s not bulky yet tough enough to withstand daily use. I should also mention that this is not an advertisement for Stanley tape measures. I just like using them.

The length of a box is always the longest dimension. The width is perpendicular to the length and shares the same plane. The depth is the measurement from top to bottom.

Be sure to record these measurements in inches and round to the nearest whole inch. For example:

6.00 to 6.49 rounds down to 6 inches
6.50 to 6.99 rounds up to 7 inches

Important: Box bulge needs to be accounted for when referencing a box’s outside dimensions. If any of the panels of the box are bulging, be sure to measure to the tip of the bulge and not just to the edges of the box.

Below we have two example measurements:

Box length measurement measured to the edge of a box

Above: the length measurement to the edge of the assembled box reads 24" on the tape measure.



 Above: The length measurement to the bulge of the assembled box reads 24+5/16" on the tape measure.


Since this measurement to the bulge of this particular box is below 24+1/2", it would round down to 24". 24" is the measurement we would use as the length measurement when creating the shipping label.

How To Calculate A Box’s Volume

The formula for measuring the cubic volume of a box can be determined by multiplying it’s outer dimensions together.

Box Volume = LxWxH

For example – if a box measures 18” X 18” X 18”, then the volume would be 5832 in.3. This box volume measurement is needed in order to determine it’s dimensional weight.


What is Dimensional Weight?

Dimensional weight is a calculated measurement that takes into account a box’s density (think shipping a box of feathers compared to shipping a box of rocks). Even though a box of feathers may weigh very little, it may be relatively expensive to ship depending on the volume of the box.

How is dimensional weight calculated?

To calculate dimensional weight for UPS, divide the box volume by the static divisor issued by UPS. As of 4/14/2021, these static divisors are:

139 for Daily Rates
166 for Retail Rates

The formulas for calculating dimensional weight depending on your applicable rates are:

Dimensional Weight for Daily Rates = Box Volume/139
Dimensional Weight for Retail Rates = Box Volume/166


The selection of which divisor to use will depend on the rates that apply to you.

Example: The dimensional weight of an 18” X 18” X 18” box if we were to ship with UPS’ Retail Rates would be:

Dimensional Weight for Retail Rates = 5832 in.3/166 = 35.13 lbs.

Important: Notice that the dimensional weight calculation does not take into account the actual weight of the box. This means that even when left empty, an 18” X 18” X 18” box has a dimensional weight of 35.13 lbs.

How To Determine The Billable Weight Of A Shipment

The billable weight of a shipment is determined by comparing the actual weight of a shipment to it’s dimensional weight. The larger of the two will be the box’s billable weight.

Since an 18” X 18” X 18” box has a dimensional weight of 35.13 lbs., if the actual packed weight is less than this amount, then it will be billed at 36 lbs. (rounded up to the next lb.). This is why we must consider the actual weight of the product that we want to ship when looking for a box to ship it in. The proper planning around a shipping box and it's selection can save you a considerable amount of money in instances where you are able to sufficiently pack and protect your product within a box that brings dimensional weight and actual weight in-line with each other. Ideally, we want to select a box that gets charged for it's actual weight and not it's dimensional weight.

Heeva Asefvaziri, CPP
Heeva Asefvaziri, CPP

Hi, there! I am the Founder/CEO of Flush Packaging. I've designed structural packaging since 2012 primarily for large companies. Flush was born out of my desire to design and make protective, purpose-built packaging products accessible to small businesses.

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