All tools / Carton dimensioning

Carton dimensioning.

Two jobs in one tool: convert internal dimensions to external (or back) using flute caliper, and see the dimensional weight so shipping cost surprises show up while the carton is still on the screen.

Inputs.

Dimensions in inches, weight in pounds. Enter whichever dimensions you have and the tool converts to the other.

I have

Length (in)

Width (in)

Height (in)

Board

Actual shipping weight, packed (lb)

External dimensions (L x W x H)16.31 x 12.31 x 10.31 in

Cubic volume, external2,071 cu in (1.20 cu ft)

Length plus girth61.6 in

External dimension adds roughly two board calipers per axis. Carriers measure the outside of the carton, so always run dim weight on external dimensions, and round each dimension up to the next whole inch the way the carriers do.

Dimensional weight.

Dim weight = (L x W x H, rounded up per axis) divided by the carrier's divisor. You are billed the greater of actual and dimensional weight.

Carrier basis	Divisor	Dim weight (lb)	Billable (lb)

Dim weight vs actualActual weight governs

Divisors move. As of July 12, 2026, the postal service joined the two major parcel carriers at a 139 divisor (applied to packages over 1 cubic foot), while retail and counter rates commonly still use 166. All the major carriers now round each dimension up to the next whole inch before applying the formula, which this tool does too. Confirm the current divisor in your carrier agreement before quoting freight, since negotiated contracts often carry a better one.

Disclaimer: These tools were built at my desk to keep the answers I need in one place. I’m sharing them in the hope that they make your design process a little easier too. The math is checked against published standards and real-world experience, but specs change and materials vary. If you spot anything that seems off, please email me at donna@donnakadell.design and I’ll take a look.

Enjoy.