Amazon FBA dimensional weight: units and inbound cartons
Two weights matter to an FBA seller. The shipping weight of each unit sets the fulfillment fee; the billable weight of the cartons you send to Amazon sets what the carrier charges you. Both use 139 in³/lb, but on different boxes.
- Unit dimensional weight
- Length × width × height of the packaged unit in inches ÷ 139
- 2-inch minimum
- Width and height count as at least 2 in for small bulky, large bulky and extra-large items
- Shipping weight
- Unit weight for small standard; the greater of unit and dimensional weight for large standard, bulky and extra-large up to 150 lb
- Inbound boxes
- At most 36 × 25 × 25 in and 50 lb, unless the box holds one oversize item
- Inbound freight
- Billed by the carrier on each box under its own rule (UPS and FedEx: 139, sides rounded up)
- Source
- Amazon Seller Central (US) help pages, checked 28 October 2026
The unit: shipping weight for the fulfillment fee
Amazon measures each unit as packaged and sorts it into a size tier. The tier decides whether the fee uses the unit weight alone or the greater of unit weight and dimensional weight. These are the US tiers from 15 January 2026:
| Size tier | Largest size (in) | Weight limit | Shipping weight |
|---|---|---|---|
| Small standard | 15 × 12 × 0.75 | 16 oz | Unit weight |
| Large standard | 18 × 14 × 8 | 20 lb | Greater of unit and dimensional weight |
| Small bulky | 37 × 28 × 20; length + girth 130 | 50 lb | Greater of the two; width and height at least 2 in |
| Large bulky | 59 × 33 × 33; length + girth 130 | 50 lb | Greater of the two; width and height at least 2 in |
| Extra-large | Anything larger or heavier | None | Greater of the two up to 150 lb (width and height at least 2 in); unit weight above 150 lb |
For large standard and bulky items the weight limit applies to the greater of unit weight and dimensional weight, so a light but bulky unit can move up a tier because of its box.
Three worked units
- Glass jar, 16.6 × 13.3 × 7.7 in, 6.6 lb. 1,700.01 in³ ÷ 139 = 12.23 lb. That is more than the unit weight, so the fee is looked up in the 12 to 12.25 lb band, not at 6.6 lb.
- Whiteboard, 40 × 1 × 25 in, 4.5 lb. It is a bulky item, so its 1 in thickness counts as 2 in: 40 × 2 × 25 = 2,000 in³ ÷ 139 = 14.39 lb, against 7.19 lb at its real thickness.
- The same product in a shallower box. At 12.2 × 12 × 4.3 in and 3.6 lb its dimensional weight is 4.53 lb, so that is used. In a 3.2 in deep box it is 3.37 lb, below the unit weight, so the fee falls to the 3.6 lb unit weight.
Amazon uses its own measurements when they differ from yours, and fees are charged by weight band (the examples on Amazon’s shipping weight page use quarter-pound bands), so check the result in Seller Central before repackaging.
The carton: sending inventory to Amazon
Boxes going to an Amazon fulfillment center, by parcel carrier, LTL or truckload, must stay within:
| Limit | Value | Exception |
|---|---|---|
| Box size | 36 in long × 25 in wide × 25 in high (91.44 × 63.5 × 63.5 cm) | A box holding a single item longer than 36 in, sized close to that item |
| Box weight | 50 lb (22.68 kg) | A single item over 50 lb: Team Lift labels on the top and sides; over 100 lb: Mechanical Lift |
| Jewelry and watches | 40 lb per box | |
| Recommended minimum | 6 × 4 × 1 in and 1 lb | Smaller boxes can delay receiving |
Within those limits the carrier bills each box on its own. Under UPS Daily Rates or FedEx (139, each side rounded up), 8 cartons of 24 × 16 × 12 in at 28 lb are 4,608 in³ ÷ 139 = 33.15 lb each, billed 34 lb: 272 lb for the shipment against 224 lb on the scale. A box at Amazon’s maximum size, 36 × 25 × 25 in, has a dimensional weight of 161.87 lb, so it is billed 162 lb even at the 50 lb weight limit: fill large boxes or use smaller ones.
Open these cartons with the UPS rule
Measure the cartons in centimetres? The calculator converts them to inches before rounding, the way UPS and FedEx do. Mixed carton sizes are covered in how to calculate dimensional weight for multiple boxes.
What this does not cover
- Fulfillment fee amounts, price bands, the inbound placement fee and storage fees.
- Apparel and dangerous goods, which have their own fee rules, and marketplaces outside the US.
- Rates of Amazon’s partnered carriers, which are quoted in Seller Central for each shipment.
Sources
Amazon Seller Central: Dimensional weight; Amazon Seller Central: Shipping weight; Amazon Seller Central: Shipping and routing requirements. Read 28 October 2026; Amazon updates these pages without a version number.
Related
Last updated: 28 October 2026. Billable weight only: surcharges, minimum charges and your negotiated rates are not included.