Girth is not circumference of the item
It describes the box, not what is inside it. A guitar in a snug case and the same guitar in a wardrobe carton produce very different girth figures, and only the carton one counts.
The measurement that sets limits
How to measure girth of a package
Girth is the distance around the box at its thickest point, which for a rectangular carton means twice the width plus twice the height. UPS puts the formula this way: to determine girth, use 2x Width plus 2x Height, then add the length, the longest side, to get the total size (per ups.com, checked 2026-07-28).
Formula quoted from the carrierFour cartons worked outThresholds with sources
Length never counts twice
The longest side is the length and stays out of the girth loop. Getting that one thing right fixes most of the arithmetic people get wrong.
Five steps, no mystery
- 1. Find the longest sideThat side is the length. It is the one measurement that never enters the girth loop, and mixing it in is the single commonest mistake.
- 2. Measure the other two sidesThose are width and height. Which is which does not matter, because both get doubled.
- 3. Double each and add themTwice the width plus twice the height gives you girth on its own. USPS words the same arithmetic differently, as length plus twice the width plus twice the height, but the total is identical.
- 4. Add the length back inThat total is length plus girth, and it is the figure every published size limit and oversize threshold is written against.
- 5. Measure the outside, and round upTape, flaps and bulges count. Carriers measure the carton as it presents itself on the belt, not as it was sold flat.
Four real cartons through the formula
These are the boxes we actually quoted on the Newark to Atlanta lane on 2026-07-28, so the arithmetic below has real prices sitting behind it rather than invented dimensions.
| Carton | Length | Girth | Length plus girth | Cheapest quote that day |
|---|---|---|---|---|
| 12 x 10 x 6 in, 5 lb | 12 in | 32 in | 44 in | $13.52 |
| 16 x 14 x 10 in, 16 lb | 16 in | 48 in | 64 in | $20.50 |
| 20 x 16 x 12 in, 32 lb | 20 in | 56 in | 76 in | $32.09 |
| 24 x 18 x 14 in, 50 lb | 24 in | 64 in | 88 in | $45.01 |
Every one of those four clears every threshold below with room to spare, which is worth seeing: ordinary cartons rarely trip an oversize rule. The trouble starts with long thin things, because one 100 inch dimension can breach a limit while the box still holds very little.
What the number is measured against
- USPS. Every service caps at 70 lb. Ground Advantage, Media Mail, Library Mail and Parcel Select run to 130 inches of length plus girth, while Priority Mail and Priority Mail Express stop at 108. On Ground Advantage and Parcel Select, passing 108 inches moves the parcel into oversized pricing rather than refusing it (Notice 123 and usps.com, checked 2026-07-28).
- UPS. The outer limits are 150 lb, 165 inches of length and girth combined, and 108 inches on a single side. A Large Package Surcharge attaches when length plus girth passes 130 inches, or length passes 96 inches, or cubic size passes 17,280 cubic inches, or weight passes 110 lb, and it carries a 90 lb minimum billable weight. Additional Handling triggers include a longest side over 48 inches or a second-longest side over 30 inches, and a cubic size over 10,368 cubic inches. UPS lists those triggers without amounts on the page we read, so no dollar figure for them appears here (ups.com, checked 2026-07-28).
- FedEx. The Oversize charge applies to packages that exceed 96 inches in length or 130 inches in length and girth, with a 90 lb minimum billable weight. The 2026 United States package services amounts are $255.00 in zone 2, $275.00 in zones 3 and 4, and $320.00 in zones 5 and 6 (FedEx 2026 surcharge and fee changes, effective January 5, 2026).
Two of those three cap a single side at or under 108 inches, which is the practical ceiling for anything long. If your item is over eight feet on its longest dimension, no parcel network will take it and the conversation moves to freight.
Two wordings, one answer
UPS writes twice the width plus twice the height, then add length. USPS writes length plus twice the width plus twice the height. They produce the same total, so a figure worked out for one carrier transfers directly to the other.
Round up before you compare
A carton at 47.5 inches of length plus girth is not worth arguing about, but one at 107.5 is. Round each side up to the whole inch before adding, and treat borderline results as over the line.
Girth questions, answered
How do you calculate girth?
Double the width, double the height, and add those two figures together. The length, meaning the longest side, is left out of girth and added afterwards to give length plus girth, which is the figure carriers publish their limits against.
What is length plus girth on a 24 x 18 x 14 in box?
Eighty-eight inches. Girth is twice 18 plus twice 14, which is 64, and adding the 24 inch length gives 88. That clears the 130 inch USPS ceiling and the 108 inch oversized-pricing line comfortably.
Does girth use the inside or the outside of the box?
The outside, measured as the parcel actually presents itself, including tape and any bulge in the flaps. Carriers measure what goes down the belt rather than what the box was sold as.
At what size does a package become oversized?
It depends on the carrier. USPS moves Ground Advantage and Parcel Select into oversized pricing above 108 inches of length plus girth, while UPS applies a Large Package Surcharge above 130 inches and FedEx applies an Oversize charge above 130 inches or 96 inches of length.