Package girth calculator
Girth is the distance around your package the short way. Enter three measurements in any order and this works out which side counts as the length, what the girth is, and whether length plus girth is inside each carrier's cap.
How girth is calculated
- Sort your three measurements. The longest becomes the length.
- The other two become width and height.
- Girth is 2 × width + 2 × height — the loop around the package.
- Length + girth adds the longest side to that loop.
Because girth uses the two shorter sides, the order you type the numbers in does not matter. A 20 × 10 × 5 box and a 5 × 20 × 10 box are the same box.
Worked example
A box measuring 20 × 10 × 5 inches.
- The longest side is 20 in, so that is the length.
- Girth is 2 × 10 + 2 × 5 = 30 in.
- Length + girth is 20 + 30 = 50 in.
- That is comfortably inside every cap we hold a rule for.
Edge cases worth knowing
- Girth is not the perimeter of the biggest face. It deliberately excludes the longest side, which is why a long thin tube can be inside the weight limit and outside the size limit.
- Rotating the box changes nothing. The formula always picks the longest side, so there is no orientation that lowers length + girth.
- Measure the outside, including bulge. An overstuffed box measures larger than the flat carton it came from.
- Caps vary by service, not just by carrier. USPS Ground Advantage allows more than most USPS mail, and FedEx Ground Economy allows less than FedEx Ground.
Common questions
- What is girth in shipping?
- The distance around your package perpendicular to its longest side. In numbers, twice the width plus twice the height.
- Which side is the length?
- The longest one. Carriers define it that way, so you cannot choose a different side to get a smaller number.
- Why do carriers cap length plus girth instead of volume?
- Because it catches awkward shapes. A long narrow package is hard to handle and hard to load even when its volume is modest.
- My package is over the cap. What now?
- A squarer box with the same volume has a smaller length plus girth. If the contents cannot be repacked, check whether another service allows more — the table in your result shows every cap we hold.