Calculator
Dimensional weight checker
Carriers bill on whichever is greater: what the package weighs, or what its volume implies. Most sellers only ever check the first one.
Package
Result
The arithmetic
Dimensional weight is length × width × height, divided by a divisor set by the carrier. Whichever is greater — actual or dimensional — is what you are billed on. That is the whole formula, and it is why a box of pillows can cost more to ship than a box of bolts.
| Step | Calculation |
|---|---|
| Volume | length × width × height |
| Dimensional weight | volume ÷ divisor |
| Billable weight | the greater of actual and dimensional |
| Density | actual weight ÷ volume — below the divisor threshold, volume wins |
Divisors are set by carrier and contract and change over time. 139 is the figure most commonly cited for US domestic parcels, but confirm the divisor in your own rate agreement rather than assuming it.
A worked example
The same product in two boxes, at a divisor of 139. Actual weight 2.4 lb in both cases — only the packaging changed.
| Box A: 12 × 10 × 8 in | Box B: 9 × 7 × 5 in | |
|---|---|---|
| Volume | 960 in³ | 315 in³ |
| Dimensional weight | 960 ÷ 139 = 6.91 lb | 315 ÷ 139 = 2.27 lb |
| Actual weight | 2.4 lb | 2.4 lb |
| Billable weight | 6.91 lb (dimensional wins) | 2.4 lb (actual wins) |
| Cubic feet, for storage | 0.556 ft³ | 0.182 ft³ |
Box A is billed at nearly three times the weight of Box B for the identical product, and occupies roughly three times the storage volume every month it sits in a warehouse. Neither cost appears on the supplier's invoice, and both are decided before the first unit is made.
What this calculator assumes
- The divisor is yours to confirm. 139 is the most commonly cited US domestic figure, but it is set by carrier and contract and it changes.
- Dimensions are of the packed unit as shipped — measured on a real sample, not taken from a drawing. Suppliers quote design dimensions; carriers measure what arrives.
- Billable weight rounds up. The calculator shows the raw figure; your invoice will round.
- Marketplace size tiers are a separate calculation using the same principle. This tool gives you the freight side; the fulfilment size tier comes from the marketplace's own table.
- No packaging weight is added. Enter the weight of the packed unit, including the box and any dunnage.
Why this matters more than it looks
- Packaging is a margin decision. An inch of unnecessary void space on each dimension can move you a whole band. That cost recurs on every unit, forever.
- Rounding is brutal at the boundary. Billable weight rounds up. Being 0.05 over a boundary costs the same as being 0.9 over.
- Marketplace size tiers work on the same principle. Amazon assigns a size tier from packaged dimensions and weight, and the tier is the biggest single driver of fulfillment cost. Crossing a boundary by a fraction is expensive in exactly the same way.
- Check before you order packaging, not after. Once 5,000 boxes are printed, this becomes a cost you live with.
Where this number goes next
- Storage — cubic feet from the same box dimensions drive four separate charges, every month.
- The 2026 fee changes — size tier and weight together set the fulfilment fee.
- Landed cost — where freight on billable weight becomes a per-unit figure.
- Packaging and SIPP — where packaging design stops being a freight question and becomes a fee question.
Frequently asked
Which divisor should I use?
The one in your carrier agreement. 139 is commonly cited for US domestic parcels, but divisors differ by carrier, service level and contract, and they change. Confirm yours rather than trusting a default.
Does Amazon use dimensional weight for FBA?
Amazon assigns a size tier from packaged dimensions and unit weight, and that tier drives the fulfillment fee. The principle is the same — volume can cost you more than mass — but the specific tables are Amazon's. Check your ASINs in the Fee and Economics Preview report.
How much can I realistically save by shrinking a box?
It depends entirely on whether the change crosses a boundary. Shaving half an inch may save nothing, or it may drop a whole band. That is why checking before ordering packaging matters more than shaving in general.