Dimensional weight can be one of the most frustrating and confusing parts of running an eCommerce site

Dimensional weight is like the ghost of your middle school math teacher came back to haunt you with the worst word problem imaginable.  

If Suzie is mailing a package that is 8x4x2 inches and weighs 8 pounds, and Bobby is mailing a package that is 12x12x8 inches and weighs 2.5 pounds, which one costs $8 less to ship?

Before you rush to find a calculator, an Algebra textbook and a paper bag to hyperventilate into, keep reading. 

We’ve created this guide to help answer your frequently asked questions about dimensional weight for shippers. We’ll first take a look at what weight is and how it’s calculated before exploring how you can use your newfound knowledge of dimensional weight to decrease your shipping costs.

What is dimensional weight?

Dimensional weight, also known as DW or dim weight,  is a calculation used by carriers to convert a package’s length, height, and width into a weight figure. 

So instead of using the package’s actual weight, carriers use this calculation? Not so fast. 

Some carriers like to have their cake and eat it too. They will use whichever value is larger. For example, a heavy item in a small package will be charged based on its actual weight while a lightweight item in a large package will be charged based on its dimensional weight.

How is it calculated?

So what’s the magical formula that converts dimensions into weight?

Dimensional Weight = (Length x Weight x Height) ÷ Divisor

For all numbers, you’ll need to round up to the nearest whole number.

The divisor you’ll use is based on the carrier and your rate. We’re taking a look at the divisor you’ll use for measuring the dimensions in inches. The divisor is different for centimeters.  

Currently, DIM Weight applies to Priority Mail packages 1 cubic foot or larger shipping to zones 5-9. The new policy expands the use of dimensional weight and decreases the divisor. 

After June, USPS will use a divisor of 166 and will apply DIM Weight to all services except First Class package service, Parcel Select Lightweight, and Flat Rate packages.  boxes. 

Let’s look at an example using FedEx or UPS’s 139 divisor.

Package Actual Weight: 5 pounds

Dimensions: 12x10x8

Dimensional Weight = (12 x 10 x 8) ÷ 139 = 6.9

The dimensional weight rounds to 7 pounds. Since the DIM weight is larger than the actual weight, the package will be billed for 7 pounds.

Why did carriers start using dimensional weight?

How often have you opened a huge box to find a small item surrounded by a ton of packing material? This is a carrier’s worst nightmare. 

The package does not weigh that much, but it’s taking up a ton of space that could be filled by other packages. 

Around 2013 as more shoppers moved online, carriers were struggling with the increase in packages. Shippers were paying close attention to their package weights, but not the size of the packages.  At the time the typical e-commerce package was composed of 40 percent fillers or air. FedEx and UPS trucks which could haul over 45,000 pounds were frequently weighing in under 25,000. 

Carriers were already using dimensional weight for express and air services and some international shipping. They expanded it to domestic ground service to charge for space the growing number of e-commerce packages occupied. 

What difference can Dim weight make?

Smart shippers need to pay attention to dimensional weight. It can make a huge difference in your shipping costs. Check out this example of how much it would cost to mail a 3-pound package in three different sized boxes:

Dimensions8x4x212x10x816x16x12
Weight333
DIM Weight (UPS/FedEx)1723
Billable Weight323 
Cost12.3517.1039.23

*Example costs based on shipping a package from Los Angeles to Dallas using FedEX Ground rates. 

Dimensional weight can have a huge impact on your final shipping cost. If you don’t consider dimensional weight, you could easily run into over or under charges. 

Let’s go back to our example above: if you were shipping a 3-pound item and charged the customer shipping based on the actual weight, but shipped it in the medium-sized box, you’ve undercharged the customer for shipping by $4.75. 

Another thing to consider is that when you use too large of a package, not only do you pay more based on the dimensional weight, you’re more likely to experience issues with damaged goods and packages. Loosely packed items are more likely to shift and get damaged in transit. Additionally, you’ll also end up paying more for the actual packaging as larger boxes typically cost more and you’ll need to use more filler material.  

How to avoid losing money with dimensional weight shipping

Now that you know what dimensional weight is and how it affects your rates, what can you do to trim your shipping costs? Follow these five tips for reducing your package DIM weight and saving on shipping.

Tip 1: Reduce your box sizes

This may seem a little obvious, but the first thing you should do is reevaluate your packaging. 

Try to pack items as compactly as possible. If you’re filling half of the box with packing peanuts or airbags, then you’re likely overpaying to ship the item. 

Shippers sometimes make the mistake of having too few box sizes to choose from. You may think you’re saving money but not ordering box sizes that you don’t frequently use, but you could actually be paying more if you’re shipping items in a much larger box.

Tip 2: Use polybags or padded envelopes when possible

If your items can ship safely in a poly bag or padded envelope, ditch the box. 

This is especially helpful for clothing retailers. If a carrier is using dimensional weight, envelopes or polybags will frequently be cheaper than boxes. 

If you’re currently shipping with USPS, you might want to consider switching to poly bags or flat rate envelopes before the postal service expands the use of DIM weight.

Tip 3: Pay attention to surcharges

People sometimes assume that if they’re paying for DIM weight, they won’t be charged for oversized packages. It makes sense, right? 

You’re already paying a rate that’s based on the space the package takes up, but unfortunately, that’s not the case. 

Review your carriers’ rates carefully so you can plan for any oversized package surcharges.

Tip 4: Shop for different carriers and rates

The expanded use of dimensional weight by the United States Postal Service is an excellent reminder that you should periodically review your carrier choices and rates. 

Shop around and make sure you’re getting the best options. 

We’ve launched the ShipperHQ Marketplace to take some of the legwork out of managing your relationship with over 30 shipping carriers and providers. Make sure to explore it on the ShipperHQ dashboard.

Tip 5: Calculate DIM Weight at checkout

If your inventory includes a lot of variety in the size and weight of products, you’re going to need some help accurately calculating shipping costs at checkout. If you don’t, you’ll end up under or overcharging customers for shipping. 

We built ShipperHQ to help make shipping easier and that includes dimensional weight. With ShipperHQ, you can set dimensional rules and define box sizes to get more accurate rates based on the dimensions of individual products and your packing options. 

By comparison, the native shipping calculators on many platforms will default to calculate shipping based only on weight, in which case you’ll end up undercharging for shipping. 

If the platform does calculate dimensional weight, it might divide orders into separate packages, or sum the total dimensions of every product in the order to get a dimensional weight – both methods will return extremely high shipping costs. 

The built-in calculations for dimensional weight might handle one or two items, but as both the items theselves and the number of items in an order increase, it’s more likely the built-in calculations will be significantly skewed. ShipperHQ’s algorithms match the product dimensions to your box sizes so you get a quote based on the most efficient way to pack and ship an order. 

Recap: Dimensional Weight Basics

At this point, we’ve covered more numbers and math than an episode of Sesame Street. To summarize the basics on dimensional weight:

  • Carriers use dimensional weight to charge for the space a package occupies.
  • Make sure you know when your carriers use dimensional weight and how they calculate it. 
  • Avoid under or overcharging for shipping by using ShipperHQ to accurately calculate your shipping costs at checkout
  • Pack smart and tight to decrease dimensional weight. 

For additional cost-cutting tips, check out our top 5 ways to save money on eCommerce shipping while still delighting customers.