Carriers charge by the greater of a box's actual weight and its dimensional (DIM) weight — so a big, light box can cost far more than the scale says. Enter your box size and weight to see the billable weight before you pay.
Dimensional weight is a pricing trick carriers use so that bulky, lightweight packages don't ship cheaply just because they're light. They calculate a "weight" from the box's size — (length × width × height) ÷ a divisor — and bill you the greater of that and the actual scale weight. A box of pillows weighs almost nothing but takes up truck space, so DIM weight makes you pay for the space.
Multiply the three dimensions in inches to get cubic inches, then divide by the carrier's divisor — commonly 139 for domestic UPS and FedEx retail, and 166 for applicable USPS packages. Round up to the next whole pound. A 12 × 12 × 12 inch box is 1,728 cubic inches; divided by 139 that's about 12.4, rounded to a 13-pound DIM weight. If the box actually weighs 3 pounds, you're still billed for 13.
The fix is right-sizing the box: use the smallest carton that safely protects the item, and cut excess void fill. Dropping a box below a divisor threshold can save a surprising amount. This is exactly the kind of thing worth checking before you print a label, especially if you ship regularly.
Divisors vary by carrier, service, and account, and change periodically — 139 and 166 are the common published figures, but negotiated accounts and international services can differ. This tool is a planning estimate; confirm your carrier's current divisor for exact billing.
A pricing figure based on package size, not actual weight. Carriers bill the greater of the two, so a large light box is charged as if heavier. DIM = (L × W × H) ÷ a divisor, commonly 139 domestic.
Multiply length × width × height in inches, divide by the divisor (139 for most UPS/FedEx, 166 for applicable USPS), and round up. You're billed on whichever is greater — DIM or actual.
Right-size the box: use the smallest carton that safely fits, and cut excess void fill. That's the most effective way to lower DIM charges.