If you've ever had a package surcharged after delivery — sometimes weeks later — there's a good chance length plus girth was the reason. It's the single most misunderstood number in parcel shipping, partly because the formula seems trivial and partly because every carrier defines its thresholds slightly differently.
This guide does three things: it explains why length plus girth exists as a concept, walks through the exact math (including the tube case, which trips most people up), and lays out current 2026 thresholds for seven major carriers side by side.
Why length plus girth exists
Parcel carriers operate vehicles and conveyor systems built around average package dimensions. A typical truck trailer is sized to fit a predictable mix of boxes; a typical conveyor sorter has rollers spaced for boxes between 6 and 30 inches long. When packages fall outside those expectations — extremely long, extremely wide, or extremely irregular — they have to be diverted, handled manually, or refused entirely.
Length plus girth is a way of capturing the "footprint" of a package in a single number. A long, thin package (a fishing rod) and a short, fat package (a heavy cube) can both cause handling problems, but volume alone doesn't capture this — a fishing rod might have low volume but be impossible to fit on a conveyor. Length plus girth penalizes both extremes by adding the longest side to twice the perimeter of the cross-section.
Carriers use it to do two things: trigger oversize surcharges (extra revenue to cover manual handling), and refuse packages that exceed the absolute limits of their network entirely.
The math, with worked examples
For a rectangular box, the formula is:
girth = 2 × (width + height)
length + girth = length + 2 × (width + height)
The "length" is always the longest dimension; "width" and "height" are the two shorter ones. Carriers do not care which one you call width and which you call height — only that you've identified the longest side correctly.
Worked example 1 — a guitar case. 45 × 17 × 6 inches. Length is the longest: 45. Width and height are 17 and 6. Girth = 2 × (17 + 6) = 46. Length plus girth = 45 + 46 = 91 inches. That's under USPS's 108-inch limit, so it ships USPS Priority Mail without oversize fees.
Worked example 2 — a small heavy cube. 18 × 18 × 18 inches. Length is 18 (any dimension, since they're equal). Girth = 2 × (18 + 18) = 72. Length plus girth = 18 + 72 = 90 inches. Also under 108 — interesting how a "compact" cube ends up close to the same threshold as a long thin item.
Worked example 3 — a fishing rod tube. A cylindrical tube 84 inches long, 6 inches in diameter. For cylinders, girth = π × diameter ≈ 3.14 × 6 = 18.85. Length plus girth = 84 + 18.85 ≈ 103 inches. Still under USPS's 108 — but only by 5 inches. A 90-inch rod tube would be over.
How seven major carriers compare in 2026
| Carrier | Max L+G | Surcharge starts | Max single side |
|---|---|---|---|
| UPS Ground | 165 in | 130 in | 108 in |
| FedEx Ground | 165 in | 130 in | 108 in |
| USPS | 108 in | 84 in | 108 in |
| DHL Express | 157 in | 120 in | 120 in |
| Royal Mail | 118 in | 80 in | 60 in |
| Canada Post | 118 in | 100 in | 78 in |
| Australia Post | 55 in | 40 in | 41 in |
The traps
A few mistakes account for nearly all of the post-delivery surcharges I've seen people hit.
Measuring the box before packing. A box that measures 30 × 12 × 12 empty might measure 31 × 13 × 13 after you've packed it and the seams have bulged. Carriers measure the package as presented, not what the box label claims. Always measure after sealing.
Forgetting that carriers round up. If your calculated length plus girth is 130.4 inches, UPS will treat it as 131. Half an inch can mean a surcharge.
Assuming a tube is the same as a box. The girth of a cylinder is its circumference, not 2 × (width + height). A 6-inch diameter tube has girth 18.85 inches — much smaller than a 6 × 6 box's girth of 24. This sometimes works in your favor, but it surprises people.
Forgetting protrusions. Handles, stickers, and protruding labels count. If you've wrapped a package and the bow on top adds an inch, it counts.
What to do if you're close to a threshold
Use the shipping calculator to see exactly where you stand against each carrier, then choose the carrier with the most headroom. If you're at 109 inches and USPS won't take it, you've got plenty of room on UPS or FedEx Ground. If you're at 166 inches, you're past UPS and FedEx Ground entirely — at that point you're shipping freight, not parcel.
Reducing one dimension by an inch (by repacking, removing unnecessary padding, or using a more snug box) can move you from surcharged to standard rates. On a single shipment that's $50–$170 saved; if you ship in volume, it's worth a few minutes of repacking.