| Marketplace | Units | Formula | Divisor |
|---|---|---|---|
| United States | inches / pounds | (L × W × H in) ÷ 139 | 139 |
| International (EU, UK, JP, CA, AU) | cm / kg | (L × W × H cm) ÷ 5,000 | 5,000 |
Worked example (US): a box 12 × 8 × 4 in = 384 in³. 384 ÷ 139 = 2.76 lb. If the product's actual shipping weight is 10 oz (0.625 lb), Amazon bills 2.76 lb — dimensional weight wins. ⚡ Try this case live
Worked example (international): a box 30 × 20 × 10 cm = 6,000 cm³. 6,000 ÷ 5,000 = 1.2 kg. If actual weight is 0.4 kg, Amazon bills 1.2 kg. ⚡ Try this case live
The 2026 large standard-size bands show the cost of a dimensional jump:
| Billable weight | Fee ($10–50 tier) | Fee (> $50 tier) |
|---|---|---|
| 0.75 lb (actual 10 oz, small box) | $4.20 | $4.46 |
| 2.76 lb (same product, 12×8×4 box — clears 2.75, bills at 3 lb) | $6.67 | $6.93 |
That one packaging choice adds $2.47 per unit before fuel surcharge, advertising or storage. On 1,000 units it is $2,470 of margin — invisible unless you model it.
The free FBA profit calculator does this automatically: enter real dimensions and weight, and it computes dimensional weight, picks the band, and applies the 3.5% fuel surcharge on top.
Enter length, width, height and weight — the calculator computes dimensional weight (÷139 US / ÷5,000 international), detects the size tier and fee band, and shows the fulfillment fee plus surcharge in the itemized breakdown.
Open the calculator with the 12×8×4 box example →
Related reading: Amazon FBA Fees 2026: Complete Guide, How to Calculate FBA Profit Margin 2026, and how to reduce FBA fulfillment fees once your bands are mapped.
Amazon bills the greater of actual weight and dimensional weight. US: (length × width × height in inches) ÷ 139. International: (length × width × height in cm) ÷ 5,000. A 12×8×4-inch box bills at 384 ÷ 139 = 2.76 lb dimensional weight even if the product weighs 10 oz.
The US divisor is 139 (inches to pounds) and the international divisor is 5,000 (cm to kg). Using the wrong divisor understates billable weight by about 12%, which is how a loose box quietly becomes a $2.47-per-unit problem.
Dimensional weight applies whenever it is greater than actual weight. This is common for large, light packages — a 10 oz product in a 12×8×4 box bills at 2.76 lb, which clears the 2.75 lb band and lands in the 3 lb large-standard rate ($5.85–$6.67) instead of the 0.75 lb band ($3.38–$4.20).
Right-size your packaging: test every SKU against the 15×12×0.75 in small-standard and 18×14×8 in large-standard limits, remove air from boxes, and consider lighter inserts. A 1-inch reduction on two sides can drop you a fee band and save $1–2 per unit.
No — small standard-size items (15×12×0.75 in, under 1 lb) are billed on actual shipping weight. The catch: the moment any dimension crosses those limits, the product moves to large standard, where dimensional weight applies and loose boxes cost real money.
US uses inches and divisor 139, giving dimensional weight in pounds. International uses centimeters and divisor 5,000, giving kilograms. Always use the divisor for the marketplace you ship to — using the wrong one can misprice a product by a full fee band.