Package size and weight limits by carrier
Measure first. Then compare prices.
Measure the box before you compare prices. Some carriers refuse an over-limit parcel outright and others divert it to freight, and a light, bulky box may be billed on dimensional weight instead of actual weight. Two things move that cost: the dimensions you pack to, and the carrier's divisor.
Four carriers, four sets of limits
USPS, UPS, FedEx, and DHL stop at different weights, different lengths, and different length-plus-girth figures — and convert cube to billable weight with different divisors.
all quoted Saved box sizes, quoted the same way twice
Store the boxes you actually pack into, so the dimensions that drive dimensional weight are entered once rather than guessed per order.
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.
Measure the box first. Then let the price argue.
A rate comparison that starts at price is comparing carriers that cannot all take the parcel. Enter the packed dimensions and the weight, and the carriers whose ceilings the box exceeds drop out before anything is priced. What is left is a list of quotes that can all actually be bought, each already billed on the greater of actual and dimensional weight.
Mailer 12x9x3 · Small box 12x12x12 · Tall box 18x14x12 — saved once, reused on every order
- Dimensions
- 18 x 14 x 12 in
- Cube
- 3,024 cu in
- Actual weight
- 6 lb
- Length + girth
- 70 in
Measure the box packed and taped, at its widest point. The dimensions you type are the dimensions you are billed on, and a guess made on a busy evening is a reweigh a fortnight later.
Checks the box against what each carrier accepts.
- Computes length plus girth properly — length plus twice the width plus twice the height
- Converts cube to dimensional weight at each carrier's own divisor
- Drops the carriers whose weight or size ceilings this parcel exceeds
- Flags the oversize and additional-handling thresholds the box is close to
The quoted amount leaves your balance. If the carrier later remeasures the parcel, the difference posts as its own ledger entry rather than an unexplained charge — which is how you find out a box needs re-sizing.
Price the parcel you actually packed.
Not the one you guessed.
Dimensional weight is computed from numbers you type. Everything below exists to make those numbers consistent, visible, and checked against four sets of carrier limits before you spend anything.
Saved box sizes,
one prepaid wallet
Store the parcels you actually ship in, so the same product goes out on the same measured dimensions every time. Labels are bought from a prepaid balance funded by card, Apple Pay, Google Pay, ACH, or crypto, with no monthly minimum to print.
Billy does
the girth arithmetic
Length plus twice the width plus twice the height, converted to dimensional weight at each carrier's own divisor, on every quote. Billy drafts the shipment from a pasted order, a screenshot, or a spoken address and asks for the box rather than assuming one.
Billed weight shown,
not just entered weight
The quote tells you whether you are being priced on the parcel's actual weight or on its cube, which is the difference between a box you should keep and a box you should shrink. One all-in number per carrier, and that exact amount leaves your balance.
Ineligible carriers
drop out before price
USPS, UPS, FedEx, and DHL stop at different weights and different length-plus-girth figures, so the honest carrier list for a large box is shorter than four. Quoting all of them against the measured parcel is what turns a limit into a filter instead of a returned shipment.
UPS $12.48 FedEx $13.22 DHL $14.10 USPS $11.79 Dimensions over
the REST API
Send parcel dimensions with the rate call and get back the eligible services with billed weight resolved, on unlimited calls on every plan. Remeasures arrive as their own adjustment records over a signed webhook, so a script can spot the SKU whose box is consistently wrong.
Size and weight limits, answered
- What is the heaviest package USPS will accept?
- Seventy pounds, across every domestic class. That is a hard ceiling rather than a surcharge threshold: a parcel above it is not mailable, so it is refused at acceptance or returned rather than being carried at a higher price. UPS and FedEx accept substantially heavier parcels on their ground services, which is the single most common reason a seller who has only ever used USPS discovers a second carrier.
- How do I measure length plus girth?
- Length is the longest side. Girth is once around the other two sides, which is twice the width plus twice the height. So the figure carriers ask for is length plus twice the width plus twice the height, not the sum of the three sides. Measure the box packed and taped, at its widest bulge, not flat and empty — the version the carrier measures is the one on the conveyor.
- What is dimensional weight and when does it apply?
- Dimensional weight converts the space a parcel occupies into a billable weight: length times width times height, divided by the carrier's divisor, rounded up. You are billed on whichever is greater, the actual weight or the dimensional weight. UPS and FedEx apply it to essentially every parcel; USPS applies it only to parcels above one cubic foot and only on the more distant zones, which is why a large light box is where the carriers diverge most.
- Why does the same box cost different amounts at different carriers?
- Three reasons stack. The carriers use different divisors, so the same cube converts to different billable weights. They apply dimensional weight at different points, so one carrier may bill your box on actual weight while another bills it on cube. And their oversize and additional-handling thresholds sit at different measurements, so a box can be ordinary at one carrier and surcharged at the next. Quoting all four against the same measured box is the only way to see which of those three is biting.
- What happens if my package is over the limit?
- It depends on the carrier, and the difference is money rather than inconvenience. USPS refuses an over-limit parcel: it is not mailable, so it is rejected at acceptance or returned to you. UPS and FedEx generally still move it, as an over-maximum-limits parcel at a charge that has nothing to do with the rate you were quoted, or by diverting it to their freight service. A refusal costs you a day. A diversion costs you a number you never agreed to.
- What box size keeps me under the dimensional-weight threshold?
- For USPS, anything under one cubic foot is never dimensional-weight billed, and one cubic foot is a twelve-inch cube — so a box smaller than 12 by 12 by 12 sits outside the mechanic entirely. For UPS and FedEx there is no such floor, so the lever is the divisor arithmetic itself: shaving an inch off the longest dimension of a mid-sized box removes a couple of hundred cubic inches and can drop a whole billable pound. Right-sizing your boxes is a bigger lever for a small seller than any rate negotiation.
Measure once. Save the box.
Quote four carriers.
Enter the packed dimensions and see which carriers can actually take the parcel, what each one will bill it as, and what it costs all in.
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