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Dimensional Weight Calculator (Amazon FBA, ÷139)

Amazon dim weight = L×W×H ÷ 139, with a 2-in floor on width and height for bulky tiers. See which side governs your billable weight. Free, runs in your browser.

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Measure the unit as it will be packed — the box, not the product.

Dimensional weight and actual weight as two bars; the taller one is what the fee is computed on Dimensional weight L × W × H ÷ 139 Actual weight what the scale reads 2.95 lb 0.80 lb 2-in floor applied to width and height you are billed on the taller bar
Why the taller bar wins: the fee is computed on the greater of the two, never a blend. That is why losing weight on a big light item changes nothing, while a smaller box changes everything — and why a flat item can be billed on a thickness it does not have.

The two rules that produce surprising dim weights

The 2-inch floor on width and height. For Small Bulky, Large Bulky, Overmax and Extra-Large, Amazon assumes the two shorter sides are at least 2 in. Flat items — placemats, decals, fabric, anything shipped stretched — get billed on a phantom thickness. A 30 × 0.5 × 9 in banner is billed as 30 × 2 × 9. Standard tiers have no floor; the same banner at 12 × 6 × 0.5 in would use raw dimensions.
Whether the floor applies is decided by size, not by tier name. The rule switches on when any sorted side exceeds 18 / 14 / 8 in — the Large Standard limits. A light, bulky-looking item still pays standard dim weight until a side crosses that line; a compact item in a heavy tier never gets the floor.
Billable weight is a max, not a blend. Every pound above the dim weight is free; every cubic inch above the actual-weight equivalent is free. That is why shaving packaging down to the next-lowest dim-weight bracket — or splitting one dense item into its own shipment — can step the fee down in a way per-unit tweaks never will.

Divisor: 139 cubic inches per pound — Amazon's US retail divisor, verified 2026-09-28. Freight forwarders use different ratios (167–200 kg per CBM for air and express, 1000 for sea); that is a separate calculation — see the CBM and chargeable-weight calculator.

Where this number goes

Dim weight feeds the FBA fulfillment fee through billable weight, and it feeds freight quotes through volumetric weight — two different ratios applied to the same box. A unit whose dim weight exceeds its actual weight pays the dim weight to Amazon, and its carton pays volumetric weight to the forwarder. The workbench runs both, side by side, against your real carton plan.

Check your whole shipment in the workbench Size tier calculator

Everything computes locally in your browser. No upload, no account.

Other calculators in this set

FBA Size Tier CalculatorWhich fee schedule your unit lands on CBM & Chargeable Weight CalculatorChargeable units per channel, rounding included Freight Class CalculatorNMFC class from density, pallet counted in Shipping Cost CalculatorThe three numbers every quote depends on Pallet CalculatorCartons per pallet, deck height included Cubic Feet CalculatorL x W x H, and what freight does with it

Frequently asked questions

What is dimensional weight?

A notional weight worked out from the volume a package occupies rather than from what it weighs. Carriers use it so that a large, light box pays roughly what the space it displaces is worth. Every carrier bills on the greater of actual and dimensional weight, never on both and never on a blend.

How do you calculate dimensional weight?

Multiply the three sides together and divide by a divisor. Amazon's US retail divisor is 139 cubic inches per pound, so an 18 x 12 x 10 in box is 2,160 divided by 139, about 15.5 lb. Freight forwarders work in metric and use their own ratios instead, which is a different calculation entirely.

What is the 2-inch minimum on width and height?

On the bulky tiers Amazon assumes the two shorter sides are at least 2 in, so a genuinely flat item is billed for a thickness it does not have: a 30 x 0.5 x 9 in banner is charged as 30 x 2 x 9. Standard tiers have no such floor. The rule switches on when a sorted side passes the large-standard limits, not when the tier name sounds bulky.

Is billable weight the average of actual and dimensional weight?

No, it is the greater of the two. Every pound above the dimensional weight is free, and every cubic inch above the actual-weight equivalent is free. That asymmetry is what makes cutting packaging down to the next dimensional-weight bracket worth more than an equivalent cut in the product's own weight.

When can I ignore dimensional weight?

When the item is dense enough that actual weight exceeds dimensional weight, which covers most metal, glass and liquid products in small packs. The calculator tells you which one governs: if actual weight wins, no amount of repacking will move the fee and only real weight reduction will.

Do freight forwarders use the same divisor as Amazon?

No. Amazon divides cubic inches by 139 to reach pounds. Forwarders multiply cubic metres by a channel ratio: about 200 kg per cubic metre for international express, 167 for air consolidation and 1000 for sea. The same carton can therefore look cheap on one channel and expensive on another.

How do I reduce dimensional weight?

Only by reducing volume, because the divisor is fixed. The longest side is usually the fastest win, since an inch off it removes more cubic inches than an inch off either short side. Where the 2-in floor applies, the two short sides are already assumed to be that tall, so making them genuinely thinner saves nothing and only the longest side is worth attacking.