How to use the dimensional weight calculator
- Choose your carrier or enter a custom divisor from your shipping account.
- Measure the box’s length, width and height at the longest points, including bulges.
- Enter the actual weight of the packed box and the number of boxes.
- The billable weight is what the carrier will charge you for.
The formula
US carriers: DIM weight (lb) = L × W × H (in, each rounded to nearest inch) ÷ Divisor UPS / FedEx divisor = 139 USPS divisor = 166 (only over 1,728 in³) International (metric): Volumetric weight (kg) = L × W × H (cm) ÷ 5,000 (or 6,000) Billable weight = larger of actual and DIM weight, rounded up
Worked example
A 12 × 12 × 12 inch box of pillows weighing 5 lb:
- Volume = 1,728 in³
- UPS / FedEx: 1,728 ÷ 139 = 12.43 → billed as 13 lb
- USPS: exactly one cubic foot, so DIM pricing doesn’t apply → billed as 5 lb
- In a 14 × 12 × 12 box, USPS would charge 2,016 ÷ 166 = 12.1 → 13 lb
Common box sizes (UPS / FedEx, divisor 139)
| Box (inches) | Volume | DIM weight |
|---|---|---|
| 8 × 6 × 4 | 192 in³ | 2 lb |
| 10 × 8 × 6 | 480 in³ | 4 lb |
| 12 × 12 × 6 | 864 in³ | 7 lb |
| 12 × 12 × 12 | 1,728 in³ | 13 lb |
| 16 × 12 × 12 | 2,304 in³ | 17 lb |
| 18 × 18 × 18 | 5,832 in³ | 42 lb |
| 24 × 18 × 18 | 7,776 in³ | 56 lb |
How to cut shipping costs
- Right-size your boxes: going from a 12-inch cube to a 10-inch cube cuts the DIM weight from 13 lb to 8 lb.
- Use poly mailers or padded envelopes for clothing and soft goods.
- Compare carriers: USPS’s higher divisor and its one-cubic-foot exemption often make it cheaper for light, bulky items.
- Flat rate boxes ignore weight and size within limits — useful for small, heavy items.
- Negotiate: high-volume shippers can often get a higher divisor (for example 166 or 194) from UPS or FedEx.
- Build it into your prices: include the real billable-weight cost when you set product prices and shipping charges.
Why carriers use dimensional weight
Trucks and planes fill up by space as well as weight. A large box of light items takes the room of a much heavier package, so carriers charge for whichever is greater. UPS and FedEx have applied dimensional weight to all ground packages since 2015, and both reduced their standard divisor to 139 in 2017. Surcharges for large packages and additional handling apply on top, so check each carrier’s current service guide for big or unusually shaped boxes.
Pallets and LTL freight are priced differently, by freight class and density, so this calculator is meant for parcels.