freightcalcsAmazon dimensional weight calculator
Divisor 139 in³/lb for FBA fulfilment fees and Amazon Buy Shipping. Part of freightcalcs.com.
Divisor 139 in³/lb for FBA fulfilment fees and Amazon Buy Shipping. Part of freightcalcs.com.
"Amazon dimensional weight" means two different things, and sellers routinely conflate them. FBA fulfilment fees are charged on the greater of a unit's actual weight and its dimensional weight — this is Amazon billing you to store and pick the item. Amazon Buy Shipping is Amazon reselling carrier labels, where the carrier's own divisor applies. This page covers the FBA calculation, which is the one that quietly reshapes your unit economics.
2026 change: Amazon extended dimensional-weight-based fulfilment fees across all major size tiers. Low-density products that previously escaped dim rating on smaller tiers are now assessed on it.
The formula is L × W × H in inches ÷ 139, rounded up to the next whole pound, then compared against actual unit weight.
Formula: L × W × H ÷ 139, rounded up to the next whole pound. Fee weight = greater of unit weight and dimensional weight. Units under 12 oz or over 150 lb are billed on actual weight only.
A 14 × 10 × 8 in boxed product weighing 1.5 lb:
| Step | Calculation | Result |
|---|---|---|
| Volume | 14 × 10 × 8 | 1,120 in³ |
| Dimensional weight | 1,120 ÷ 139 | 8.06 lb |
| Round up | — | 9 lb |
| Fee weight | greater of 1.5 lb and 9 lb | 9 lb |
Your fulfilment fee is calculated as if the unit weighed nine pounds. For a product with a thin margin, this single line can be the difference between profitable and not — and it is driven entirely by box dimensions, which you control.
| Condition | How the fee is calculated |
|---|---|
| Unit under 12 oz | Actual weight only — exempt |
| Unit over 150 lb | Actual weight only — exempt |
| Everything in between | Greater of actual and dimensional weight |
The 12 oz floor is the one worth designing around. If a light product can be packaged to stay under 12 oz shipped weight, it avoids dim rating entirely regardless of how bulky the box is.
These are separate charges calculated separately, and a unit can be dim-rated on one and not the other:
| FBA fulfilment fee | Amazon Buy Shipping | |
|---|---|---|
| Who charges it | Amazon | The carrier, sold through Amazon |
| Divisor | 139 | The carrier's — see UPS, USPS, FedEx |
| Measured on | The individual unit | The outbound shipping box |
Note the last row. FBA measures the sellable unit; Buy Shipping measures whatever box leaves the building. For merchant-fulfilled orders through USPS, remember dim weight only applies above one cubic foot.
139. Amazon multiplies the unit's length, width and height in inches, divides by 139, and rounds up to the next whole pound, then bills the fulfilment fee on whichever is greater — that figure or the unit's actual weight.
Amazon extended dimensional-weight-based fulfilment fees across all major size tiers. Low-density units that previously escaped dim rating on smaller tiers are now assessed on it, so bulky lightweight products saw fee increases.
Yes. Units under 12 oz and units over 150 lb are billed on actual weight only. Everything between those bounds is billed on the greater of actual and dimensional weight.
No. The FBA fulfilment fee is Amazon's own charge on the sellable unit. Amazon Buy Shipping passes through the carrier's calculation on the outbound box, using that carrier's divisor and rules. They are separate charges and often produce different weights.
Reduce box dimensions — the fee is driven by volume, not weight. Removing slack fill, using a right-sized carton, or redesigning packaging to drop a size tier are the levers. Getting a light unit under the 12 oz threshold removes dim rating altogether.
Yes, to the next whole pound. A calculated 8.06 lb dimensional weight becomes 9 lb for fee purposes.
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