Package size and weight limits by carrier

Hard maximums by carrier: weight, length, and length plus girth

Every rate comparison has a step before price, and most sellers skip it. A carrier that cannot legally accept your parcel is not a cheaper option, it is not an option — and the four carriers stop in different places. USPS caps every domestic class at the same weight and applies two different length-plus-girth ceilings depending on the class, which catches sellers out constantly: the class most people reach for first is not the class with the largest size allowance. UPS and FedEx accept parcels several times heavier on their ground services, and impose their own separate ceilings on the longest side and on length plus girth. DHL Express states its limits per piece in metric, which is worth knowing before you convert a pallet-adjacent box in your head.

The practical consequence is that the set of carriers you are choosing between shrinks as the box grows, and it shrinks in an order that is not obvious. A heavy, compact parcel eliminates USPS long before it approaches anyone else's ceiling. A light, enormous parcel can be perfectly acceptable to USPS on one class, unmailable on another, and fine at UPS and FedEx but expensive there for a completely different reason. The figures themselves are in the dated block at the bottom of this page; the shape of the rule is what you need in your head while you are picking a box.

How to measure length plus girth (most sellers get this wrong)

Girth is not a side. It is the distance once around the parcel at its thickest point, perpendicular to the length — which for a rectangular box is twice the width plus twice the height. So the figure a carrier asks for is length plus twice the width plus twice the height. The common error is adding the three dimensions together, which systematically underestimates and produces a number that clears every published limit right up until the carrier measures it.

Work an example. A 24 by 14 by 12 inch box has a length of 24 and a girth of twice 14 plus twice 12, which is 52, giving 76 inches — well inside every carrier's allowance. Now take a 40 by 20 by 18 box: length 40, girth 76, total 116 inches. That single box is over the smaller USPS class ceiling, under the larger one, and comfortably inside the UPS and FedEx limits. Nothing about the box changed; the eligible carrier list did.

Two measurement habits are worth more than any of this arithmetic. Measure the box packed, taped, and sitting the way it will sit on a conveyor, because a bulging side is what gets measured downstream, not the flat-pack dimensions printed on the carton. And measure to the next whole inch up rather than down — carriers round in their own favour, and the gap between your rounding and theirs is a classic source of a post-shipment correction you did not budget for.

When you are billed on dimensional weight instead of actual weight

Carriers sell space on a vehicle, not mass. A box full of packing peanuts occupies the same floor as a box full of bolts, so carriers convert volume into a billable weight: length times width times height, divided by a published divisor, rounded up. You are billed on whichever is greater, the actual weight or that dimensional weight. This is not a surcharge, it is a different basis for the base rate, which is why it rarely appears as a line item and instead shows up as a rate that does not match what you expected.

Where the carriers differ is in when the mechanic engages at all. UPS and FedEx apply dimensional weight to essentially every parcel on their standard services. USPS applies it only above a cubic-foot floor and only to the more distant zones on its main parcel classes. That single difference produces most of the surprises a small seller meets: a large, light parcel travelling a short distance can be billed on actual weight at USPS and on cube at UPS, and the two quotes will look like they are pricing different shipments, because in a real sense they are.

Worked through: an 18 by 14 by 12 box is 3,024 cubic inches. Divided by a divisor of 139 and rounded up, that is 22 billable pounds — for a parcel that might genuinely weigh six. If the contents actually weighed 30 pounds, dimensional weight would be irrelevant and you would be billed on 30. The moment to notice this is while you are choosing the box, not while you are reading the quote.

Packing to a divisor: the box size that keeps you under the threshold

There are exactly two levers on dimensional weight. The divisor belongs to the carrier and you cannot move it. The dimensions belong to you and you can move them today, which makes right-sizing the highest-leverage shipping change available to a small seller — considerably more effective than trying to negotiate a rate at low volume.

The arithmetic is unusually kind here, because cube is a product of three numbers. Taking one inch off the longest side of that 18 by 14 by 12 box removes 168 cubic inches, which is more than a billable pound at a divisor of 139. Dropping a soft-goods order out of a box and into a poly mailer removes the problem entirely, because a mailer that conforms to its contents has almost no cube to convert. And for USPS specifically there is a bright line worth designing around: stay under one cubic foot and the mechanic never engages. One cubic foot is a twelve-inch cube, so any box smaller than 12 by 12 by 12 is outside dimensional-weight billing at USPS regardless of zone.

The operational half of this is consistency. Dimensional weight is computed from what you enter, so a box guessed at from memory on a busy evening quietly becomes a reweigh a fortnight later. GoatLabels lets you save the box sizes you actually pack into, so the same product ships on the same measured dimensions every time and the quote you compare is the quote you get. Once the boxes are standard, buying against them in bulk is a spreadsheet job — bulk shipping labels from a CSV covers that flow.

Exceeding a limit: outright refusal versus diversion to freight

Going over a limit does not mean the same thing at every carrier, and the difference is the whole reason to check before you pack. USPS treats its ceilings as mailability rules: an over-limit parcel is refused at acceptance or returned to you, so the cost is a wasted day, a wasted label, and an unhappy buyer, but not an unexpected invoice. UPS and FedEx generally still move the parcel — as an over-maximum-limits shipment carrying a charge that bears no relationship to your quote, or by diverting it into their freight service, where it is priced as freight. The parcel arrives. The bill is not the one you agreed to.

Below those hard ceilings sit the graduated fees, and they are the ones that actually catch small sellers because they trigger on parcels that feel normal. Additional handling fires on length past a stated figure, on weight past a stated figure, and on packaging that is not a standard corrugated box — tubes, drums, anything wrapped in plastic, anything the automated sort has to be pulled off. A large-package surcharge fires on length plus girth past a stated figure and typically carries a minimum billable weight, so a light oversized box is billed as though it were heavy. Both stack on top of dimensional weight rather than replacing it, and both are much larger during announced peak windows. The thresholds are in the dated block below; the seasonal timing of the increases is covered on shipping surcharges explained.

If a carrier reweighs or remeasures after the parcel is already moving and bills the difference, that is a post-shipment adjustment with its own detection and dispute path — covered in full on carrier billing adjustments. If you are choosing between the budget ground tiers for a large box, the crossover is worked through on cheapest ground shipping services, and the general case for quoting rather than defaulting is on cheap shipping labels.

Limits and divisors, checked 2026-08-03

Everything that can rot is in this block and nowhere else on the page. Structural limits move rarely; divisors and surcharge thresholds are re-set by carriers at least annually and occasionally mid-year.

• USPS — 70 lb maximum weight on every domestic class. Ground Advantage accepts up to 130 inches combined length and girth; Priority Mail and Priority Mail Express stop at 108 inches. Over the limit is not mailable, so the parcel is refused or returned.
• UPS and FedEx — 150 lb per package on standard ground and express services, 108 inches maximum length, 165 inches maximum length plus girth. Over those ceilings the parcel is handled as an over-maximum-limits shipment or diverted to freight rather than refused.
• DHL Express — per-piece weight and length limits published in metric; convert before you assume a large box qualifies.
• Dimensional divisors — 139 for UPS and FedEx US domestic parcels in inches and pounds; 166 for USPS, which applies dimensional weight only to parcels over one cubic foot (1,728 cubic inches) and only on the more distant zones; 139 in imperial or 5000 in centimetres and kilograms for DHL Express.
• Large package surcharge — triggers at UPS and FedEx on length plus girth above 130 inches, and applies a minimum billable weight regardless of what the parcel actually weighs.
• Additional handling — triggers on stated length and weight figures and on non-corrugated or irregular packaging. Stacks on top of dimensional weight.

Verify every figure above against the carrier's own current service guide rather than an aggregator before packing to a threshold — divisors in particular. Review cadence: annual, plus a re-check on any announced rate or divisor change.