Multi-box shipments
Multi-box dimensional weight calculator.
Enter up to six boxes. See each box billed on actual or dimensional weight, the USPS Ground Advantage total, and FedEx billable weight per package and per shipment.
Boxes
Result
What this page answers
Most dimensional-weight calculators take one package. A shipment of four boxes is not four copies of the same answer: one box may sit under the 1 cubic foot line where USPS ignores dimensions, another may be billed on volume, and FedEx may total the shipment two different ways. This page does the arithmetic box by box and then adds it up each way the carriers describe.
Use it after you have decided how to pack. To compare packing choices for the same items, use the mixed-cart estimator instead.
How it is calculated
USPS. Each box ships on its own label and is priced as its own Ground Advantage parcel from the Notice 123 retail table: the greater of actual weight and dimensional weight (only over 1,728 cubic inches, each dimension rounded up, divided by 139, rounded up, 70 lb cap). The total is the sum of the boxes.
FedEx. Per package, each box is length x width x height with every dimension rounded up, divided by 139, compared with actual weight, and rounded up to a whole pound. Per shipment, the volumes of all pieces are added first and divided by 139 once, then compared with the total actual weight. FedEx states that dimensional weight applies on a per-package or per-shipment basis depending on the service and shipment type, so the page shows both.
Worked example: a 24 lb two-box order
Box A is 24 x 18 x 12 in and 10 lb; box B is 14 x 10 x 8 in and 6 lb. Zone 6.
FedEx per package: A is 5,184 cubic inches, 5,184 / 139 = 37.30, so 38 lb billable. B is 1,120 cubic inches, 1,120 / 139 = 8.06, so 9 lb even though it weighs 6 lb. Sum: 47 lb. Per shipment: 6,304 cubic inches / 139 = 45.35, against 16 lb actual, so 46 lb. The two bases differ by 1 lb.
USPS: box A is over 1,728 cubic inches, so dimensional weight is 38 lb and the zone 6 price for 38 lb is $108.05, plus $4.50 because the longest side is over 22 in and $21.00 because the box is over 2 cubic feet: $133.55. Box B is under 1 cubic foot, so USPS bills its actual 6 lb at $22.45. Total $156.00 on 44 lb of billable weight. The same small box is billed 9 lb by FedEx but 6 lb by USPS.
Where this stops
USPS Ground Advantage retail only; no Priority Mail, UPS, commercial or cubic prices, discounts or surcharges. FedEx is shown as billable weight, not price. Which FedEx basis applies to a given service, account or shipment is stated in your agreement and the Service Guide, not decided here. Dimensions are outside measurements of the packed box.
Sources
- USPS Notice 123 Price List, effective October 4, 2026: USPS Ground Advantage Retail parcels table and its notes (retrieved 2026-10-26)
- USPS Domestic Mail Manual 133, section 1.4 Dimensional Weight Price for Low-Density Parcels; steps marked [7-12-26] (retrieved 2026-10-26)
- FedEx Service Guide, effective January 5, 2026 and updated September 11, 2026: Dimensional Weight, p. 135 (retrieved 2026-10-26)
Carriers revise prices and rules during the year. Confirm against the live documents before relying on a figure for a contract or a dispute. This is a calculator, not a carrier quote.
Common mix-ups
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Often assumedI can round each box measurement to the nearest inch.
What the source saysSection 1.4.2 says to round up each measurement to the nearest whole inch before multiplying. A side of 12.2 inches counts as 13, which can push a box past the 1,728 cubic inch line. [1]
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Often assumedUSPS adds the volume of all my boxes together to get one dimensional weight.
What the source saysThe steps in section 1.4.2 measure the length, width and height of one parcel and divide that parcel's volume by 139. Each parcel is therefore priced on its own, and the 70-pound cap applies to each parcel's dimensional weight. [1]
Checked against these sources on .
FAQ
Is dimensional weight calculated per box or for the whole shipment?
USPS prices each parcel on its own. FedEx says it applies dimensional weight per package or per shipment depending on the service. This page shows the per-package sum and the per-shipment total side by side.
Do I round the box dimensions?
Yes. USPS DMM 133 says to round each measurement up to the nearest whole inch. The FedEx Service Guide says any fraction of an inch is rounded up to the next-higher inch, effective August 18, 2025.
Which divisor does each carrier use?
The USPS text we read on 2026-10-26 (DMM 133 section 1.4, marked 7-12-26) divides by 139, and so does the FedEx Service Guide. If another source quotes a different USPS figure, check its revision date against the DMM.
Why is a small box billed more by FedEx than by USPS?
USPS applies dimensional weight only to parcels over 1 cubic foot. The FedEx Service Guide applies it to every shipment in customer packaging, so a 1,120 cubic inch box that weighs 6 lb is billed 9 lb by FedEx.