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Dimensional weight calculator for Amazon FBA

Amazon's dimensional weight is the packaged unit's length times width times height, in inches, divided by 139. From the large standard tier up, Amazon uses it when it is greater than the unit weight; small standard items use the unit weight only. Enter your box in inches or centimeters to see both weights and the one Amazon uses.

Your packaged unit

Measure the unit as it ships to Amazon, in its packaging, not the master carton.

Length unit

Weight unit

Dimensional weight
8.29 lb
Unit weight
3.00 lb
Weight Amazon uses
8.29 lb

Size tier: Large standard. Dimensional weight is greater, so Amazon uses 8.29 lb. About 64% of that is empty space in the box.

See the 2026 placement fee for this tier

The formula

Dimensional weight (lb) = length (in) x width (in) x height (in) / 139

Weight Amazon uses = the greater of unit weight and dimensional weight

  • Small standard: unit weight only. Dimensional weight does not count.
  • Large standard: the greater of the two.
  • Small bulky, large bulky and extra-large up to 150 lb: the greater of the two, with width and height counted as at least 2 inches each.
  • Extra-large over 150 lb: unit weight only.

Worked examples

Calculated with the same code as the calculator above.

16 x 12 x 6Unit weight (lb): 3.00Dimensional weight (lb): 8.29Size tier: Large standardWeight Amazon uses (lb): 8.29
12 x 9 x 4Unit weight (lb): 2.00Dimensional weight (lb): 3.11Size tier: Large standardWeight Amazon uses (lb): 3.11
10 x 8 x 4Unit weight (lb): 4.00Dimensional weight (lb): 2.30Size tier: Large standardWeight Amazon uses (lb): 4.00
10 x 6 x 0.5Unit weight (lb): 0.50Dimensional weight (lb): 0.22 (not used)Size tier: Small standardWeight Amazon uses (lb): 0.50
30 x 12 x 1Unit weight (lb): 1.00Dimensional weight (lb): 5.18Size tier: Small bulkyWeight Amazon uses (lb): 5.18

The last row is a flat box: 1 inch tall counts as 2 inches in the small bulky tier, so its dimensional weight doubles. To see what each tier pays to send units to Amazon, use the placement fee calculator.

Dimensional weight FAQ

How does Amazon calculate dimensional weight for FBA?

Length times width times height of the packaged unit, in inches, divided by 139. The result is in pounds. Amazon then uses the greater of the unit weight and the dimensional weight, except for small standard items and extra-large items over 150 lb, which use the unit weight only.

Does dimensional weight apply to small standard items?

No. Small standard items are billed on the unit weight only. From large standard up to extra-large items of 150 lb, Amazon uses whichever is greater, the unit weight or the dimensional weight.

Why does a flat box get a higher dimensional weight than I expected?

In the small bulky, large bulky and extra-large tiers, Amazon counts the width and the height as at least 2 inches each in the formula. A box 1 inch tall is calculated as if it were 2 inches tall.

Whose measurements does Amazon use?

For fees, Amazon's. When Amazon's measurements of the packaged unit differ from yours, Amazon's are used, and Amazon may measure sample units again.

Can I enter centimeters and kilograms?

Yes. The calculator converts centimeters to inches and kilograms or ounces to pounds, then applies Amazon US's formula with the divisor of 139.

How do I lower the weight Amazon uses?

When dimensional weight is the greater one, the box is carrying air. A smaller box, or a poly bag where Amazon's packaging rules allow it, lowers the dimensional weight and can move the unit to a lighter fee band or a smaller size tier.

Sources

Amazon's pages for US FBA size tiers and fees, read on the date shown.

  1. Amazon Seller Central: Dimensional weight, read October 26, 2026
  2. Amazon Seller Central: Product size tiers, read October 26, 2026
  3. Amazon Seller Central: 2026 US FBA fulfillment fee changes, read October 26, 2026

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