Dimensional (DIM) weight is a size-based weight: length × width × height, divided by the carrier's divisor, rounded up to the next pound. Carriers bill on whichever is higher, the actual weight or the DIM weight, so a large, light box can cost more than its weight suggests.
1. The formula
- Measure length, width, and height in inches, rounding each to a whole inch as the carrier specifies (most carriers round up).
- Multiply them to get cubic inches.
- Divide by the carrier's divisor.
- Round up to the next whole pound. That is the DIM weight.
- Compare it with the actual weight. The higher one is the billable weight.
2. Divisors in the U.S.
| Carrier | Divisor | When DIM applies |
|---|---|---|
| USPS | 139 | Priority Mail Express®, Priority Mail®, USPS Ground Advantage® and Parcel Select®, only for packages above 1 cubic foot (1,728 cubic inches). Each side is rounded up to the next whole inch. In effect since July 12, 2026 (the divisor was 166 before). |
| UPS® | 139 (UPS daily rates) | May apply to all UPS domestic and international package services |
| FedEx® | 139 | U.S., Puerto Rico and international shipments. Your FedEx account terms can differ. |
Divisors vary by rate type and service and change from time to time. Check the current rule with the carrier before you rely on it.
3. Divisors in Canada
| Carrier | Inches (cubic inches per lb) | Centimetres (cubic cm per kg) | Applies to |
|---|---|---|---|
| UPS® Canada | 139 (115 for domestic air) | 5,000 (4,100 for domestic air) | 115 / 4,100 for domestic air services within Canada (UPS Express Early, UPS Express, UPS Express Saver and UPS Expedited); 139 / 5,000 for all other packages, including UPS Standard |
| FedEx® Canada | 139 | 5,000 | Shipments within Canada and international |
| Canada Post | 139 | 5,000 | Priority, Xpresspost and Expedited Parcel within Canada |
Purolator® uses a cube factor instead of a divisor: 12.4 lb per cubic foot for Purolator Ground and for Express shipments that do not travel by air, and 15 lb per cubic foot for Express shipments that travel by air, unless your Purolator agreement sets a different cube factor. Purolator is available only on Canadian accounts, not U.S. accounts.
Two exceptions: For odd-shaped (non-rectangular) USPS parcels, USPS adjusts the size first: length × width × height × 0.785, then divides by 139. Canada Post Regular Parcel uses a divisor of 166 (6,000 in centimetres) instead of 139.
4. A quick example
A 20 × 20 × 20 inch box is 8,000 cubic inches. At a 139 divisor (USPS, UPS® daily rates and FedEx®) that is 58 lb of DIM weight (8,000 ÷ 139 = 57.55, rounded up), so a light item in that box is billed at 58 lb. A small 12 × 10 × 6 inch box that weighs 12 lb is billed on its 12 lb actual weight.
5. How Rollo Ship uses your dimensions
When you create a shipment, you enter dimensions and weight on the What are you shipping? screen. Rollo Ship returns rates with dimensional weight already taken into account. If the box you ship is bigger or heavier than what you entered, the carrier can re-rate the label after purchase.
Save boxes you use often as package presets (box type, dimensions and weight) so each shipment starts with the right size.
6. How to lower DIM charges
- Use the smallest box that protects the item.
- Use a soft package or poly mailer for items that don't need a box.
- Measure the packed box, including bulges.
- Compare services: some carriers apply DIM only above a size threshold.
FAQ
What is billable weight?
The weight a carrier charges for: the higher of the actual weight and the dimensional weight.
Does USPS charge dimensional weight on small boxes?
No. USPS applies DIM pricing only to packages above 1 cubic foot (1,728 cubic inches).
Why did my rate change when I changed the box size?
The new size changed the dimensional weight. If it is higher than the actual weight, the price goes up.
Can the price change after I buy the label?
Yes. If the carrier measures a larger size or heavier weight than you entered, it can re-rate the label.
Where can I calculate DIM weight?
Use the dimensional weight calculator on rollo.com.
Why shippers use Rollo Ship
- Free to start. Registering, downloading the app, comparing rates, connecting stores, importing orders and managing inventory are free. No credit card, Rollo printer purchase, contract, or minimum or maximum shipping volume.
- Built-in carrier discounts. USPS® and UPS® are built in for U.S. shippers, and Canada Post and UPS® are built in for Canadian shippers, with discounted rates. Connect your own FedEx® (U.S. and Canada) or Purolator® (Canada only) account at your own negotiated rates.
- No label fee on your first 200 labels. After that, it's 5¢ per label, down to 1¢ with Rollo Rewards. Postage still applies.
- Compare before you buy. See rates side by side and sort by best value, lowest price or fastest delivery.
- Print and ship anywhere. Labels print directly in 4x6 shipping label format on a Rollo printer, and Rollo Ship works with any compatible printer. Ship from your phone with the free Rollo app, or print over WiFi with a Rollo Wireless printer.
Quick links
- Dimensional weight calculator
- Dimensional weight vs actual weight (rollo.com guide)
- Shipping calculator
- Understanding UPS® Additional Handling charges
- Rollo Ship per-label fees explained
- Get the free Rollo app
Enter your box and compare rates in Rollo Ship.