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 2026-08-22, 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 | $33.16 |
| 24 x 18 x 14 in, 50 lb | 24 in | 64 in | 88 in | $47.42 |
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.
One long thin thing, boxed two ways, quoted 2026-08-22
A floor lamp is the ordinary version of a long thin thing. Boxed with the pole broken into two nested lengths it measures 46 x 12 x 8 in: a girth of 40 in (twice 12 plus twice 8) and a length plus girth of 86 in, clear of the lines both carriers write below. Boxed with the pole left at full length, the same lamp measures 64 x 14 x 10 in: a girth of 48 in and a length plus girth of 112 in. That crosses the 105 in line UPS and FedEx write their Additional Handling dimension trigger against, and the 108 in line where USPS Ground Advantage and Parcel Select move into oversized pricing (Notice 123, effective July 12, 2026, pe.usps.com, read 2026-08-22).
| Box | Length plus girth | UPS Ground | FedEx Ground |
|---|---|---|---|
| 46 x 12 x 8 in, 9 lb, pole nested | 86 in | $31.85 | $46.13 |
| 64 x 14 x 10 in, 12 lb, pole full length | 112 in | $69.94 | $132.64 |
Two things move together in that second row: a bigger box always carries more dimensional weight on its own, and this one also qualifies for Additional Handling once its length plus girth passes 105 in. Both carriers fold the charge into the total shown rather than breaking it out as a separate line, which is why the jump is larger than the weight difference alone would explain. UPS's and FedEx's own trigger lists and 2026 amounts are on the additional handling surcharge page.
What the number is measured against
- USPS. Every service caps at 70 lb. Ground Advantage and Parcel Select run to 130 inches of length plus girth, while Priority Mail, Priority Mail Express, Media Mail and Library Mail stop at 108. On Ground Advantage and Parcel Select, passing 108 inches moves the parcel into oversized pricing rather than refusing it (Notice 123, prices effective July 12, 2026, and DMM 201, both at pe.usps.com, checked 2026-08-22).
- 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; the amounts by zone are on the additional handling page linked above (ups.com, checked 2026-08-22).
- FedEx. The Oversize charge applies to packages that exceed 96 inches in length or 130 inches in length and girth — and, since January 12, 2026, packages over 17,280 cubic inches or 110 lb as well — with a 90 lb minimum billable weight. The 2026 United States package services amounts run from 255 USD in zone 2 through 275 USD in zones 3 and 4 and 320 USD in zones 5 and 6 to 330 USD in zones 7 and beyond (FedEx Service Guide, effective January 5, 2026, read 2026-08-22).
Two of those three draw a single-side line at or under 108 inches, which is the practical ceiling for anything long. An item past that mark stops being a parcel problem and 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.
What happens when girth pushes a package over a carrier's line?
The price jumps by more than the weight alone explains. In a live SMKlog capture on 2026-08-22, boxing the same floor lamp at 112 inches of length plus girth instead of 86 inches raised the UPS Ground quote from $31.85 to $69.94 and the FedEx Ground quote from $46.13 to $132.64, because the bigger box carries more dimensional weight and now qualifies for Additional Handling as well.