Dimensional Weight: Formula, Carrier Divisors and Examples
Dimensional weight is the weight a parcel carrier calculates from the size of a box, and it is billed whenever it exceeds the real weight. A light item in a big box pays for the air around it. We give the formula, the divisors UPS, FedEx and USPS use, one product priced in 3 box sizes, and what a 3PL does to keep the number down.
Quick summary
- Dimensional weight is length x width x height in inches divided by a divisor, and carriers bill whichever is greater, the dimensional weight or the actual weight.
- FedEx divides by 139 for US and international parcels, UPS by 139 on daily rates and 166 on retail rates, and USPS by 139 for commercial parcels over 1 cubic foot.
- Measurements are rounded to whole inches and the result is rounded up to the next whole pound, so a fraction of an inch can add a billed pound.
- In our example, one 4 lb item bills at 4 lb in a snug box, 9 lb in a stock box and 22 lb in an oversized one at UPS or FedEx.
- A 3PL cuts dimensional weight with a box range matched to measured SKU sizes, cartonization in its WMS and mailers for soft goods.
What dimensional weight is
Dimensional weight, or dim weight, is a weight a carrier calculates from the size of a parcel rather than from a scale. A truck or an aircraft fills up by volume long before it reaches its weight limit when it carries light, bulky boxes, so carriers price the space a parcel takes as well as its mass. FedEx puts the billing rule plainly: you are charged on the dimensional weight or the actual weight, whichever is greater.
The greater of the 2 is the billable weight. A 20 lb cast iron pan in a snug box bills on its 20 lb. A 2 lb pillow in a large box bills on the box.
The dimensional weight formula
- Measure the length, width and height of the packed box in inches. Length is the longest side.
- Round each measurement to a whole inch, by the carrier’s rule.
- Multiply length x width x height to get cubic inches.
- Divide by the carrier’s divisor and round up to the next whole pound.
A 14 x 10 x 8 box is 1,120 cubic inches. Divided by 139, that is 8.06, which rounds up to a dimensional weight of 9 lb. If the item inside weighs 4 lb, the carrier bills 9 lb.
Rounding is where carriers differ. FedEx rounds each side to the nearest whole inch; USPS rounds each side up. Take a box measuring 14.2 x 12.1 x 10.3 inches:
- At FedEx it becomes 14 x 12 x 10, or 1,680 cubic inches, and a dimensional weight of 13 lb.
- At USPS commercial prices it becomes 15 x 13 x 11, or 2,145 cubic inches, which crosses the USPS 1 cubic foot line and bills at 16 lb. Rounded to the nearest inch, it would have stayed under the line and been priced on actual weight.
Shipping software rates each parcel when its label is printed, the last step before carrier handoff in order fulfillment, so the dimensions it sends must be those of the packed box, not the product.
Dimensional weight divisors by carrier
| Carrier and rates | Divisor | When it applies |
|---|---|---|
| UPS daily rates | 139 | Any domestic or international package service |
| UPS retail rates | 166 | Any domestic or international package service |
| FedEx | 139 | US, Puerto Rico and international shipments |
| USPS commercial (Priority Mail Express, Priority Mail, Ground Advantage) | 139 | Parcels over 1,728 cubic inches; the 70 lb price is the cap |
UPS sets out both of its divisors in its package dimensions and weight guide: 139 for daily rates and 166 for retail rates, with dimensional weight able to apply to all its domestic and international package services. The USPS rule sits in the Domestic Mail Manual: commercial parcels over 1 cubic foot are priced on the greater of actual and dimensional weight, with each side rounded up to the whole inch, the cube divided by 139, and any dimensional weight over 70 lb charged at the 70 lb price.
A smaller divisor makes the same box heavier on paper. The 14 x 10 x 8 box is 9 lb at 139 and 7 lb at 166, so the same box bills 2 lb heavier on a UPS daily-rate account than at the retail counter.
One 4 lb item in 3 box sizes
The box is the only part of the formula a brand controls. Here is the same 4 lb item packed 3 ways:
| Box | Size (inches) | Cubic inches | Dim weight at 139 | Billable at UPS daily or FedEx | Billable at USPS commercial |
|---|---|---|---|---|---|
| Snug | 10 x 8 x 6 | 480 | 4 lb | 4 lb | 4 lb |
| Stock | 14 x 10 x 8 | 1,120 | 9 lb | 9 lb | 4 lb (under 1 cubic foot) |
| Oversized | 18 x 14 x 12 | 3,024 | 22 lb | 22 lb | 22 lb |
The stock box is the one a warehouse grabs when nobody has set a rule, and at UPS or FedEx it more than doubles the billed weight. The oversized box bills 22 lb everywhere.
Return parcels are billed the same way. A prepaid return label is priced on the box the customer sends back, so an oversized box costs the brand twice, once on the way out and again in the returns flow.
Charges that stack on a large box
Dimensional weight is only the first charge a big box draws. The same UPS guide caps a package at 150 lb, 108 inches in length and 165 inches in length plus girth, where girth is twice the width plus twice the height. Carriers also add handling surcharges for packages that are long, heavy or awkward to handle, on top of the billable weight, so a large box can pay 2 or 3 extra charges on top of its base rate.
Past the parcel limits, a shipment becomes freight. UPS describes LTL as pallet freight, typically over 150 lb, and offers Ground with Freight Pricing for multiple packages totaling 151 lb or more without a pallet. For a brand shipping bulky goods such as furniture or displays, that is the point to compare parcel and freight quotes.
What a 3PL does about dimensional weight
A 3PL chooses the box, and the box sets the postage, which on a typical parcel order costs more than every other line of ecommerce fulfillment costs combined. Four things decide how much dimensional weight its clients pay:
- Measured SKU dimensions: every SKU measured and weighed at receiving, not copied from a supplier sheet.
- A box range matched to the products: enough sizes that each common order has a box within an inch or 2 of its contents.
- Cartonization: the WMS choosing the box at the pick and pack step from item dimensions, so packers are not guessing.
- Mailers for soft goods: poly or padded mailers for apparel and textiles, which stay small and, at USPS, under the 1 cubic foot line.
Postage reaches the invoice in one of 2 ways: the 3PL passes through the carrier’s charge on its own account, often with a markup, or bills from its own rate card by zone and billable weight. Either way, the invoice or portal should show each parcel’s dimensions, actual weight and billed weight.
Frequently asked questions
What is dimensional weight?
Dimensional weight is a weight calculated from a parcel's size: length times width times height in inches, divided by the carrier's divisor. Carriers bill the greater of that figure and the actual weight, so a light item in a large box is billed for the space it takes.
What is the formula for calculating dimensional weight?
Multiply length, width and height in inches, then divide by the carrier's divisor, which is 139 for FedEx, UPS daily rates and USPS commercial prices. Round the result up to the next whole pound. A 14 x 10 x 8 box is 1,120 cubic inches, which divided by 139 is 8.06, billed as 9 lb.
How do you calculate dimensional weight for USPS?
Round each measurement up to the next whole inch and multiply them. If the result exceeds 1,728 cubic inches, or 1 cubic foot, divide by 139 and round up to the next whole pound; smaller parcels are priced on actual weight. The rule covers commercial Priority Mail Express, Priority Mail and USPS Ground Advantage parcels, and a dimensional weight over 70 lb pays the 70 lb price.
How do I calculate the dimensional weight of my FedEx package?
Measure length, width and height in inches, round each to the nearest whole inch, multiply them and divide by 139. FedEx uses 139 for US, Puerto Rico and international shipments. It bills whichever is greater, the dimensional weight or the actual weight.
What is billable weight?
Billable weight is the weight a carrier prices a parcel on: the greater of its actual weight and its dimensional weight, each rounded up to the next whole pound. A 4 lb item in a box with a dimensional weight of 9 lb is billed at 9 lb.
Why do some carriers divide by 139 and others by 166?
The divisor depends on the rate type. UPS uses 139 for daily rates, the rates business accounts pay, and 166 for retail rates. A larger divisor gives a lower dimensional weight, so the same box is billed lighter at 166.
Does dimensional weight apply to small packages?
At UPS and FedEx it can apply to any package, however small, whenever its dimensional weight exceeds its actual weight. USPS applies it only to parcels over 1 cubic foot, which makes small mailers a common choice for light soft goods.
Can a 3PL lower my dimensional weight charges?
Yes, mainly through the box: a box range matched to measured SKU dimensions, cartonization software that picks the smallest safe box, and mailers for soft goods. Ask for actual and billed weight on every parcel, because that is where a poor box choice shows up.