Dim weight calculator
Carriers bill the greater of actual weight and dimensional weight - your package's volume divided by a DIM divisor. Enter a box below to see what FedEx, UPS, or USPS will actually charge for.
Your shipment
Outer carton dimensions and the actual scale weight.
Dimensional weight = (L × W × H) ÷ divisor, rounded up to the next whole lb. Carriers bill whichever is greater: actual or dimensional weight.
You're paying for air - this shipment bills at 7 lb instead of 3 lb: +4 lb of empty box space on the invoice.
What is dimensional weight?
A trailer cubes out long before it weighs out - so carriers price space, not just mass. Every parcel gets two weights, and you pay for whichever is bigger.
Volume becomes weight
Dimensional weight = length × width × height ÷ divisor, rounded up to the next whole pound or kilogram. A 12×10×8 in box at divisor 139 is 7 lb before anything goes inside it.
You're billed the max
Billable weight = max(actual, dimensional). If the box above weighs 3 lb on the scale, the carrier still rates it at 7 lb. The 4 lb gap is empty space you're paying to ship.
Divisor 139 for FedEx & UPS
FedEx, UPS and USPS all use divisor 139 in³/lb - USPS moved from 166 on July 12, 2026 and now rounds each dimension up to the whole inch. DIM pricing applies above 1 cubic foot; international metric shipments commonly use 5000 cm³/kg.
The fix isn't a spreadsheet - it's a smaller box, chosen per order.
Since dimensional weight is pure geometry, the only durable way to stop paying for air is to pack each order into the smallest carton that actually fits it. That's a 3D bin packing problem, and it's exactly what CartonPilot's cartonization API automates: send items and your box line-up, set options.dimDivisor to your carrier's divisor, and pick the lowest-billable-weight objective to minimize what carriers actually bill - not just the box count.
In our published, reproducible benchmark that meant 44% fewer parcels and ~$11.31 saved per order at published 2026 FedEx/UPS Ground list rates (Zone 5, DIM divisor 139). Dimensions are unit-agnostic - inches, cm, whatever your WMS speaks.
{
"options": {
"objective": "lowest-billable-weight",
"dimDivisor": 139
}
}
// each shipment in the response:
"billing": {
"actualWeight": 3.2,
"dimWeight": 7,
"billableWeight": 7
}See your savings before you write code.
Paste an order (or a CSV) and the production engine shows parcels saved, box spend, and estimated FedEx/UPS Ground cost - right here.
Your order
| Item | L | W | H | lb | Qty | |
|---|---|---|---|---|---|---|
Audited against a standard 7-box corrugated line-up using a first-fit baseline vs. cartonpilot-ultra.
Add your items and run the audit to see how many parcels and how much box spend CartonPilot can cut.
Dimensional weight FAQ
What is dimensional (DIM) weight?
Dimensional weight is a pricing technique carriers use so bulky-but-light packages pay their share of trailer space. They convert a package's volume into a theoretical weight - length x width x height divided by a DIM divisor - and bill the greater of that number and the actual scale weight. A big box of pillows gets billed like a heavy box, because it occupies the same truck space.
How do I calculate dimensional weight?
Multiply the package's outer length, width, and height, then divide by your carrier's DIM divisor and round up to the next whole unit. Example: a 12 x 10 x 8 inch box is 960 cubic inches; at divisor 139 that's 6.9, which rounds up to 7 lb. If the box actually weighs 3 lb, the carrier bills 7 lb - the greater of the two.
What DIM divisors do FedEx, UPS, and USPS use?
FedEx and UPS both use divisor 139 (cubic inches per pound) for daily/list rates. USPS also uses 139 as of July 12, 2026, when it moved from 166 for Priority Mail Express, Priority Mail, Ground Advantage and Parcel Select; the same change requires each dimension to be rounded up to the next whole inch, and DIM pricing still applies only above 1 cubic foot. International metric shipments commonly use 5000 (cubic centimeters per kilogram). High-volume shippers sometimes negotiate a custom divisor - the calculator on this page supports any value.
How do I reduce dimensional weight charges?
Shrink the box. Since DIM weight is pure geometry, the only durable fix is shipping each order in the smallest carton (or carton mix) that actually fits it. Doing that by hand per order is impractical, which is why cartonization software exists: it packs each order in 3D and picks the box that minimizes what the carrier bills.
Does CartonPilot handle dimensional weight?
Yes. Pass your carrier's divisor via options.dimDivisor and every shipment in the response includes a billing block with actual, dimensional, and billable weight. There's also a dedicated lowest-billable-weight objective that chooses cartons specifically to minimize the billed weight - not just the box count.
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