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Shipping box size calculator: billable weight and annual savings from right-sizing
Compare the carton you ship in today with the smallest carton that fits your product, and see the change in dimensional weight, handling charges, list rate and annual shipping cost at your volume, after the cost of the box.
Source: FedEx Standard List Rates, the published 139 divisor and 2026 handling thresholds · FedEx Standard List Rates effective January 5, 2026; divisor 139; 2026 handling thresholds · Free, no signup
The product
The carton it ships in today
Volume and packaging cost
| Carton | Cubic in | Dimensional | Billable | List rate, zone 5 | Handling | Carton | Per package | A year |
|---|---|---|---|---|---|---|---|---|
| Current carton 18×14×12 | 3,024 | 22 lb | 22 lb | $28.28 | 0 | $1.10 | $29.38 | $587,600 |
| Right-sized carton 16×12×10best | 1,920 | 14 lb | 14 lb | $22.23 | 0 | $1.25 | $23.48 | $469,600 |
| Stock carton 16×12×12 | 2,304 | 17 lb | 17 lb | $24.07 | 0 | $1.10 | $25.17 | $503,400 |
| Stock carton 18×12×12 | 2,592 | 19 lb | 19 lb | $26.42 | 0 | $1.10 | $27.52 | $550,400 |
| Stock carton 20×16×12 | 3,840 | 28 lb | 28 lb | $34.65 | 0 | $1.10 | $35.75 | $715,000 |
In the current carton, 73% of the billable weight is air: the box bills at 22 lb and weighs 6. The right-sized carton is the product plus 1 in on every side, rounded up to the inch; whether that is enough protection depends on the product, and a carton that fails in transit costs more than any of this saves. The stock rows are common catalogue sizes that fit, priced at the current carton cost, to show how much of the saving a standard box captures. A right-sized carton that costs $0.15 more than the current one pays for itself in freight on the first package at zone 5: the extra $0.15 against $6.05 saved. Rates are FedEx Ground list rates effective January 5, 2026 with the published divisor and 2026 handling rules, before any incentive, fuel or other surcharge. Your incentive scales the transportation saving down; fuel scales it back up.
See how your agreement changes this result.
Send twelve months of shipment data with dimensions. We will measure how much of your billed weight is air by SKU and carton, price the right-sized alternatives at your rates, and show what a packaging change and a divisor negotiation are each worth.
What size shipping box should I use?
The right shipping box is the smallest carton that holds the product with enough clearance to protect it, because UPS and FedEx bill the greater of actual weight and length times width times height divided by 139. Every inch of empty space in a carton is billed as weight. An 18 by 14 by 12 inch box bills at 22 pounds whatever is in it; a 16 by 12 by 10 box bills at 14. On a 6 pound product to zone 5 that is $28.28 against $22.23 at FedEx Ground list rates, $6.05 a package, and a right-sized box also keeps the package under the 48 inch, 105 inch length-plus-girth and 10,368 cubic inch additional handling thresholds. Custom packaging is worth its extra cost when the freight saved per package, multiplied by annual volume, exceeds the difference in box price.
Worked example
A 14 by 10 by 8 inch product with 1 inch of clearance on every side needs a 16 by 12 by 10 inch carton, 1,920 cubic inches, which bills at 14 lb. Shipped today in an 18 by 14 by 12 inch carton, 3,024 cubic inches, the same 6 lb package bills at 22 lb: 73% of the billable weight is air. At zone 5 list rates that is $28.28 against $22.23, $6.05 a package. If the right-sized carton costs $1.25 against $1.10 for the current one, the net saving is $5.90 a package and $118,000 a year on 20,000 packages, and the dearer box pays for itself on the first package.
Published rates, not your agreement
The calculator prices FedEx Ground list rates before any incentive, fuel or other surcharge, at one zone; an incentive scales the saving down and fuel scales it up. It assumes the product is a rectangular solid and that the clearance entered is enough protection, which only a drop test tells you. It does not model void fill, pallet or case packs, Ground Economy, SurePost or USPS, where dimensional weight applies only over one cubic foot. The stock sizes are common catalogue cartons, not a carrier list.
Source: FedEx Standard List Rates, the published 139 divisor and 2026 handling thresholds. FedEx Standard List Rates effective January 5, 2026; divisor 139; 2026 handling thresholds.
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