How to Measure a Box – Packaging 101

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Intro to Packaging and Shipping

Measuring a shipping box might seem like an ordinary skill but today we’re going through the basics for any beginners or businesses that are new to shipping products. We’ll cover how to measure a box, figuring out the cubic size as well as other general shipping information to keep in mind before packaging your product to get it sent out to a customer. 

When packing and shipping boxes, it’s important to know how to measure a box properly in order to get the most efficient shipping rates. There are certain steps to measuring a box that will make it easier for your business and here’s everything you need to know in order to measure a box.

Inside or Outside Dimensions?

When you purchase a box from WCP or other distributors, shipping boxes are measured using the inside dimensions. This is done so that you know that your products will fit properly. When you measure a box for shipping with carriers like UPS or FedEx, you’ll be measuring the outside dimensions of the box. By using the outside dimensions it allows carriers to accurately figure out the space required for your package.

How to Measure a Box

  1. Measure the length of the box first. This is the long side of the box on the side of the longest flap.
  2. Next, turn the box 90 degrees and measure the width, which is the side with the shorter flap.
  3. Last, measure the height of the package. This will be measured with the flaps closed, from top to bottom.

*Note on measurements – Acceptable variance is +/- ⅛”.

Dimensional Weight and Shipping Your Package

Most freight companies charge by the dimensional weight of the box or the actual weight, whichever is greater. They do this so they can maximize their profits, which makes it vitally important for the shipper to have the right-sized box for your product so you don’t overspend on shipping.

How to Calculate the Dimensional Weight

  1. Multiply the length by the width by the height of the box to calculate the cubic size.
  2. Take the cubic size of the box and divide it by the shipping carrier’s divisor. For FedEx and UPS, the retail dimensional weight divisor is 139 and both DHL and USPS use 166 as the dim factor for packages less than 1,728 cubic inches (or 1 cubic foot). See carrier for more details.

For shipping companies, costs are based on the size of the box but also where the package is being shipped to. Shipping companies will charge you shipping costs based on the cubic size of the package based on the destination.  The dimensional weight needs to be exact and not rounded at all for proper shipping costs.


If you have more questions or need help finding the perfect box please reach out to your local WCP team!


Updated on 12/07/2021
Originally published 11/11/2019