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The Shipwire Blog/How to calculate dimensional weight

How to calculate dimensional weight

In some ways, the approach to calculating shipping costs seems designed to confuse. After all, billable weight sometimes does not reflect weight at all – but instead involves a tricky little concept called dimensional weight.

To insulate themselves from the cost of transporting lightweight but bulky packages, carriers calculate charges based on the greater measurement between the actual gross and volumetric weight, assuming a package meets a certain threshold size.

But you can insulate yourself from unnecessary costs, too. When you know dimensional weight is likely to be triggered – when bulk exceeds weight – you should pack to your advantage. The first step to trimming such costs, then, is understanding dimensional weight.

What is dimensional weight?
Dimensional weight has long been the standard bearer in air shipping, but it didn’t arrive in ground shipping till 2007, when many carriers began incorporating the calculation. The application of dimensional weight can therefore penalize shippers of light objects over dense objects.

The “weight” label is a bit of a misnomer. The dimensional weight – often shortened to dim weight – reflects a package’s density, or how much space a package will occupy on a carrier’s freight truck or airplane. It’s essentially a theoretical weight, what a package should or could be expected to weigh given its size.

But it isn’t quite as simple as knowing how big a package is.

To calculate the dimensional weight of a package:

  1. Measure the package. Note that the sizes indicated by a box manufacturer may not apply, as carriers want the measurements of length, width and height to reflect the package’s size at its extremes. If there’s a bulge, a warped side, or an irregular shape, the measurements should reflect all this, accounting for the most space the package can occupy. Avoid charge corrections by measuring.
  2. Get the cubic size. Multiply length x width x height.
  3. Divide by the dimensional factor. For domestic ground shipments, the dimensional factor to divide by is 166. For international air shipments, divide the cubic size by 139. This factor is subject to change (and last did so in 2011) so be sure to check out the information from carriers for updates.
  4. Round up. Carriers will round up to the nearest whole number, so you should too.


Here’s an example:
Let’s say you’re ground shipping a package via UPS. Your box measures 24″ x 18″ x 18″ and the parcel weighs 50 lbs.

  1. To find the cubic size you’ll need to multiply 24 by 18 by 18. That yields 7,776 cubic inches.
    You’re shipping ground, meaning the applicable dimensional factor is 166.
  2. Dimensional weight: 7,776 / 166 = 46.8 lbs., or 47 lbs.
  3. The dimensional weight is less than the actual weight, so the actual weight will be used.

Now let’s pretend that same box is used to ship something that weighs 10 lbs. The dimensional weight is greater than the actual weight, which means that the dim calculation of 47 lbs. will be the billable weight.

When is dimensional weight relevant?
It depends a little on your carrier, but here are a few rules of thumb: Dimensional weight is always relevant for air service. For ground service by private carriers, billable weight is influenced by dimensional weight if the cubic size of the package is 3 cubic feet (5,184 cubic inches) or larger. If it’s less than that, you can expect actual weight to be used.

Once you’ve confirmed the cubic size exceeds 3 feet and calculated your package’s dimensional weight, compare the dim weight to the actual gross weight. The greater of the two will be used to determine shipping costs.

But that isn’t all. If your package is deemed “large” — meaning the length plus girth exceeds 130 inches – carriers like UPS and FedEx will also apply a surcharge.

The United States Postal Service, meanwhile, has its own spin on the cubic size and dimensional weight issue, which can make its flat-rate mailing packages more attractive. Packages addressed to Zones 1 through 4, or going to relatively local destinations, may be subject to a so-called “balloon price”. If the length plus girth is greater than 84 inches, your package will be charged the price of a package weighing 20 lbs. Mail addressed to Zones 5 through 8, or far away, will be subject to dimensional weight principles if the cubic size is more than a foot (1,728 cubic inches).

You can explore the ins and outs of various carriers’ approach to billable shipping on their individual websites. Shipwire can also lay it out for you, and a Shipwire Free Trial can allow you to easily evaluate how your overall costs will be impacted by tweaks to your shipping materials and methods.

The reality of theoretical weight is that it’s costly. Where possible, decrease the size of the box you’re using to ship. Even shaving 1 inch can save money, and the savings only increase with greater volume.

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