Why Is Priority Mail Cheaper Than Priority Mail Cubic Sometimes?

If any online shipping software is worth its salt, it offers USPS Priority Mail Cubic as an option. Simply put, Priority Mail Cubic is the cheapest and fastest way to send small, heavy packages under 20 pounds with USPS. Anyone who takes advantage of Priority Mail Cubic enjoys better shipping rates than they would with any other service. However, there are certain times when regular weight-based Priority Mail is cheaper than Priority Mail Cubic. This is a rare case indeed, but here’s a quick breakdown of how it can happen.

Priority Mail Cubic Is Cheaper Than Weight-Based Priority Mail 99% of the Time

Before we get into it, we need to stress that Priority Mail Cubic the cheaper service nearly all of the time. Priority Mail Cubic’s pricing is based on your package’s outer dimensions, and not its weight. That means you can load up your packages with as many goodies as you want, and as long as the total weight doesn’t exceed 20 pounds, you won’t be charged for it! When you do the math, cubic rates can save you up to 90% off the retail prices you’d pay for at the Post Office.

If you did a side by side comparison of Priority Mail and Priority Mail Cubic with a variety of different packages, you’d see that cubic rates are cheaper pretty much 99% of the time. However, that other 1% still represents a small chance when Priority Mail is cheaper…and it does happen sometimes.

A Quick Example of When Priority Mail is Cheaper

Let’ say you’re shipping a 1.5 pound package with the dimensions 10x10x6″ from Phoenix to Houston. Those dimensions will put your box in the 0.4 cubic pricing tier, and the distance between the cities (roughly 1,200 miles) falls into USPS Zone 6. USPS rounds weights up to the nearest pound for regular Priority Mail, so they will classify this box as 2 pounds and charge accordingly.

Going off of USPS Commercial Pricing rates, the price for shipping this particular box Priority Mail Cubic to Zone 6 would be $11.78. However, regular weight-based Priority Mail for this same 2-pound package would only cost $9.99! This “anomaly” happens because this is a slightly larger box in a higher cubic pricing tier, and it also doesn’t weigh a whole lot.

The Rule of Thumb

Generally speaking, the heavier the box and the smaller its dimensions, the more likely it is that Priority Mail Cubic is the cheaper service. That’s because cubic rates don’t take weight into consideration—only package dimensions. When it comes to cubic rates, smaller dimensions equals cheaper prices. On the other hand, if your box isn’t super heavy and its dimensions are on the slightly larger side, weight-based Priority Mail will be the best way to go.

Learn how to calculate which cubic pricing tier your package belongs to.

The Cheapest Service is What’s Best for Your Business

At the end of the day, it doesn’t really matter which service you use to ship…as long as your business is saving the most money. Both regular Priority Mail and Priority Mail Cubic offer the same delivery window of 1-3 business days. They both come with $100 of insurance (when you use shipping software to buy postage online), and they both offer free door-to-door package tracking. In essence, the two services are exactly the same. The only difference is that the prices of one are based on a package’s dimensions, while the prices of the other are based on weight.

So, if you’re seeing Priority Mail as your selected service instead of Priority Mail Cubic on your shipping software of choice, don’t fret. You’ve just found yourself in one of those rare instances—a case of the “outliers,” as Malcolm Gladwell would say. The good news is, you’re not losing out either way!