While measuring a box might seem straightforward, there’s actually more to the process than meets the eye. Thankfully, we here at Box Genie can help you get the most precise measurements for your boxes so that you can effectively pack your products and get accurate shipping rates: 

Internal Dimensions or External Dimensions

Believe it or not, but there are actually two different sets of dimensions for boxes. There are internal dimensions that involve measuring the box from the inside. And there are external dimensions that involve measuring the box from the outside. But what’s the difference between these dimensions, and which method should you choose? 

Internal dimensions are generally used across the board because they provide the most accurate information in terms of what size items can actually fit inside the box. On the other hand, external dimensions include the size of the cardboard being used. 

As a result, external dimensions actually indicate a size that’s larger than what can actually fit inside the box. If you’re trying to achieve the perfect fit for your products, this seemingly small difference can quickly become a big problem. 

Measure the Box

Based on what you now know about internal and external dimensions, we will be using internal dimensions to measure our boxes for this article’s purpose. While these measurements might not be as easy to take, they are more accurate and, therefore, more important. So how can you measure the internal dimensions of your box? 

First of all, you should start with an open box that’s facing up. You will measure the length first by locating the longest side of the box. Take your tape measure or ruler, and measure from one corner on the longest side to the other. Make a note of the length measurement before moving on to the next one — width. 

The width of the box will be taken from the shortest side. Take your tape measure or ruler, and measure from one corner of the shortest side to the other. Make a note of the width measurement before moving on to the last one — height. 

The last remaining measurement is height, or how tall the box is. Starting from the bottom corner of the box, place your tape measure right against the surface and measure from the bottom corner to the top corner. Make a note of this final measurement so that you’re able to make your final calculations. 

Weigh the Box

While knowing the size of your box is important, knowing the weight of the box may also be necessary when you’re looking to ship out an order. This is because many carriers incorporate both size and weight into their shipping prices. 

The best method of weighing your package is to use a postal scale. However, if you don’t have a postal scale lying around, you could try using something like a kitchen scale instead. 

You may also be able to use a luggage scale or a bathroom scale if you have no other options, keeping in mind that these methods might not be as accurate. To get an accurate weight, be sure to calibrate the scale before placing the package — contents and all — onto the scale. 

It’s important to weigh the package exactly how it’s going to be shipped as seemingly small changes in arrangement, packaging materials, etc., can affect the weight. Make a note of the package’s weight before moving on to complete your shipping calculations. 

Make Your Calculations

Now it’s time to put your measurements together by completing these easy shipping calculations. 


Volume indicates how much space your box will take up and is important when determining shipping and warehousing costs. To calculate volume, you will need to multiply together your package’s length, width, and height. 

For instance, say you have a package with a length of 5 inches, a height of 3 inches, and a width of 2 inches. Your calculation for volume would be 5 x 2 x 3, which equals 30 inches cubed. 

Dimensional Weight

Dimensional weight is a common shipping calculation used by major carriers to calculate the weight of the box and the price you’ll pay for shipping. To calculate dimensional weight, you will begin by using the volume calculation covered above — multiplying together the package’s length, width, and height. 

From there, you will use the carrier’s divisor to determine the dimensional weight. Let’s use bigger numbers for this example to make it easier — a length of 15 inches, a width of 10 inches, and a height of 30 inches. When multiplied together, you get 4,500 inches cubed. 

FedEx has a domestic DIM divisor of 139 cubic inches per pound. As a result, you would divide 4,500 by 139 to get a dimensional weight of 32.37 pounds. If the actual weight of your package is less than 32.37 pounds, say 30 pounds, you would still pay for 32.37 pounds since it’s the larger number. 

On the other hand, if the actual weight of your package is 35 pounds — about three pounds above the dimensional weight of 32.37 pounds, you would then pay for 35 pounds since it’s the larger number. 

Find the Best Shipping Rates

UPS has a DIM divisor of 166 for retail customers. So let’s calculate what your dimensional weight for UPS would be based on the same numbers so that you can learn how to get the best shipping rates. When you divide 4,500 by 166, you get a dimensional weight of 27.11 — 5.26 pounds lighter than the dimensional weight of a FedEx package. 

However, the dimensional rate is just one factor to consider when you’re looking for the best shipping rates. Different carriers charge different rates for different sizes, weights, and shipping journeys. So how can you find the most cost-effective option? 

The three major carriers — USPS, UPS, and FedEx — all have shipping calculators on their websites so that you can quickly and easily get a shipping calculation based on the size, weight, destination, and origin of your package. There are also different services to choose from, including air, ground, expedited, etc. 

If you’re looking for an even better deal, then you should consider partnering with a single carrier for business purposes. For instance, USPS offers commercial pricing that provides discounts of up to 15% off retail shipping and postage prices. These commercial prices are based on bulk shipments. For instance, presorted and automation First-Class Mail requires a minimum of 500 pieces. 

FedEx offers a Small Business Program that offers discounted shipping rates to small businesses of up to 16%. Finally, UPS offers a Connect Program that provides 20% off the air and international shipments and 10% off ground shipments. 

At the same time, you need to keep in mind that the best rates don’t necessarily come with the best service. For instance, USPS retail ground usually comes with the cheapest rates, but it also takes seven days for delivery. In a world where customers expect their packages in record time, you may not be able to sacrifice speed for low prices. 

Final Thoughts on Measuring Boxes for Shipping

If measurements aren’t your thing, consider using packaging providers that give you access to all the information you need to choose the best products for your brand. For instance, Box Genie offers custom boxes in tons of different sizes — making it totally possible for you to find the right fit. 

If you need any help along the way, reach out to our experts for tailored guidance. 



  1. Package Dimensions: How to Measure a Box for Shipping | UPS
  2. What Is Dimensional Weight? | FedEx
  3. Business Shipping - Rates, Discounts, Services | USPS

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