Girth Calculator

What girth means

Carriers limit parcel size using two numbers: the length (the single longest side) and the girth (the distance around the box at its thickest point). Girth wraps the two shorter sides:

girth = 2 × (side2 + side3)

length + girth = longest side + girth

Most size limits are written as a maximum length plus girth, so that is the figure this calculator highlights.

Worked example

For a 30 × 20 × 15 in box:

1. Longest side (length): 30 in
2. Girth: 2 × (20 + 15) = 70 in
3. Length + girth: 30 + 70 = 100 in

At 100 in, that box is within the UPS, FedEx and USPS limits below, so it ships as a standard parcel rather than an oversize one.

Why carriers measure it this way

Length plus girth is a proxy for how awkward a parcel is to handle, not just how big it is. A long, thin box (a poster tube, a fishing rod case) can have a small footprint but still jam a conveyor sorter or need to be handled by hand rather than machine, so carriers cap the combined figure instead of volume alone. It also only needs a tape measure at the depot, no scale or scanner, which is why the formula has stayed the same for decades even as carriers have moved everything else onto dimensional weight.

Carrier size limits (length + girth)

Going over a limit usually pushes a package into an oversize or additional-handling tier, or it may be refused. Confirm the current limit with your carrier, since they revise these periodically.

To estimate the billed weight of the same box, use the dimensional weight calculator; for the raw cubic volume, use the box volume calculator.

A second example: an oversize case

A 50 × 24 × 20 in case, the kind used for sports or musical equipment:

1. Longest side (length): 50 in
2. Girth: 2 × (24 + 20) = 88 in
3. Length + girth: 50 + 88 = 138 in

At 138 in that case clears UPS and FedEx's 165 in limit but is already over USPS's 130 in ceiling, so the carrier you choose changes whether it ships as a standard parcel at all, not just what it costs.