Amazon’s FBA fulfillment fee depends on two things: the product’s size tier and its shipping weight. For most tiers, shipping weight is the greater of the unit weight and the dimensional weight — so packaging size feeds straight into your fee. Everything below comes from Amazon’s own Seller Central pages for 2026 (2026 US FBA fulfillment fee changes; 2026 fee changes summary).
The FBA dimensional weight formula
FBA dimensional weight (lb) = (L × W × H in inches) ÷ 139
Two details from Amazon that matter:
- For Small Bulky, Large Bulky and Extra-Large items, Amazon assumes a minimum width and height of 2 inches.
- Dimensional weight is used when it’s larger than the unit weight for Large standard, Small Bulky, Large Bulky and Extra-Large (except 150+ lb) units. Small standard and Extra-Large 150+ lb units use unit weight only.
So for a Small standard product, a bigger box doesn’t raise the fee through dimensional weight — but it can push the product out of Small standard altogether.
The 2026 size tiers
Amazon puts each product in the smallest tier whose limits it meets on every line: shipping weight, longest side, median side, shortest side and length plus girth. For tiering, shipping weight is always the greater of unit weight and dimensional weight (Amazon: Product size tiers).
| Tier | Shipping weight | Longest | Median | Shortest | Length + girth |
|---|---|---|---|---|---|
| Small standard | ≤ 16 oz | ≤ 15 in | ≤ 12 in | ≤ 0.75 in | — |
| Large standard | ≤ 20 lb | ≤ 18 in | ≤ 14 in | ≤ 8 in | — |
| Small Bulky | ≤ 50 lb | ≤ 37 in | ≤ 28 in | ≤ 20 in | ≤ 130 in |
| Large Bulky | ≤ 50 lb | ≤ 59 in | ≤ 33 in | ≤ 33 in | ≤ 130 in |
Extra-Large (0–50, 50+–70, 70+–150 and 150+ lb) is anything over the Large Bulky limits: longest side over 59 in, median or shortest side over 33 in, length + girth over 130 in, or shipping weight over 50 lb.
Small standard and Large standard are “standard size”; every other tier counts as “oversize” (that’s the split Amazon’s storage fees use). Extra-Large products up to 150 lb that exceed 96 inches on the longest side or 130 inches in length plus girth are “Overmax” and pay an Overmax handling fee from 15 January 2026.
The cliffs to watch
- 0.75 in shortest side. Amazon’s own examples show it: a 13.8 × 9 × 0.7 in phone case is Small standard; a 13 × 9 × 0.85 in T-shirt is Large standard.
- 15 × 12 in and 16 oz — the other Small standard limits.
- 18 × 14 × 8 in and 20 lb — beyond any of these, a product leaves standard size and moves to Small Bulky, where fees start at $7.55 instead of $3.73 (the $10–$50 band).
- 37 × 28 × 20 in — the Small Bulky limits; past them, Large Bulky starts at $9.35.
2026 FBA fulfillment fees
Non-peak rates, 15 January – 14 October 2026, for products priced $10–$50 (excluding apparel). Products under $10 and over $50 have their own rate columns.
| Size tier | Shipping weight | Fee per unit |
|---|---|---|
| Small standard | 2 oz or less → 14+ to 16 oz | $3.32 → $3.96 |
| Large standard | 4 oz or less → 2.75+ to 3 lb | $3.73 → $6.67 |
| Large standard | 3+ lb to 20 lb | $6.97 + $0.08 per 4 oz above 3 lb |
| Small Bulky | 0 to 50 lb | $7.55 + $0.38/lb above first lb |
| Large Bulky | 0 to 50 lb | $9.35 + $0.38/lb above first lb |
| Extra-Large | 0 to 50 lb | $26.33 + $0.38/lb above first lb |
| Extra-Large | 50+ to 70 lb | $37.32 + $0.75/lb above 51 lb |
| Extra-Large | 70+ to 150 lb | $51.32 + $0.75/lb above 71 lb |
| Extra-Large | 150+ lb | $194.95 + $0.19/lb above 151 lb |
On top of these: from 17 April 2026, a 3.5% fuel and logistics-related surcharge applies to FBA fulfillment fees. Holiday peak fees apply from 15 October 2026 to 14 January 2027 (for example, Small standard at 2 oz or less rises to $3.51 in the $10–$50 band). Products priced under $10 get Low-Price FBA rates, which Amazon says average $0.86 less.
Amazon’s own examples
| Product | Dimensions | Weights | 2026 non-peak fee |
|---|---|---|---|
| Mobile device case — Small standard, under $10 | 13.8 × 9 × 0.7 in | Unit 2.88 oz (unit weight only) | $2.49 |
| Iron — Large standard, $10–$50 | 12.6 × 6.6 × 5.5 in | DIM 3.29 lb; unit 3.35 lb → 3.25+ to 3.5 lb | $7.13 |
| Monitor — Extra-Large 0–50 lb, $10–$50 | 54 × 35 × 3.5 in | DIM 47.59 lb; unit 41 lb → 47+ to 48 lb | $44.19 |
The monitor shows the effect: 54 × 35 × 3.5 = 6,615 in³ ÷ 139 = 47.59 lb, so it’s billed in the 47+ to 48 lb band instead of the 40+ to 41 lb band its 41 lb unit weight would give. At $0.38 per lb, that’s $44.19 instead of $41.53 — $2.66 per unit from packaging volume alone.
Strategies that reduce FBA fees
1. Check the tier before you finalize packaging
Compare your packed dimensions and weight against the Product size tiers limits. Dropping one tier is usually worth more than any per-pound saving.
2. For Large standard and above, trim volume
Dimensional weight applies from Large standard up, so every cubic inch of packaging counts once it exceeds the unit weight. Remember the 2-inch minimum width and height for bulky and extra-large items.
3. For Small standard, watch unit weight
Small standard fees use unit weight only, stepping every 2 oz up to 16 oz. Lighter inner packaging can move a product down a step.
4. Bundle carefully
Combining products can push the bundle into a larger tier. Run the numbers for the bundle and for the items sold separately.
Storage and inventory fees
Storage is charged on volume, so packaging size matters here too. Amazon bills monthly storage on your daily average volume in cubic feet, measured on the unit packaged and ready to ship (Amazon: Monthly inventory storage fees). Base rates for non-dangerous goods:
| Period | Standard-size (per ft³) | Oversize (per ft³) |
|---|---|---|
| January – September | $0.78 | $0.56 |
| October – December | $2.40 | $1.40 |
A storage utilization surcharge is added for Professional sellers whose first US shipment was over 365 days ago, who store 25 ft³ or more per size tier, and whose storage utilization ratio (average daily volume stored ÷ average daily volume shipped over 13 weeks) is above 22 weeks. It rises from $0.44 per ft³ (22–28 weeks) to $1.88 per ft³ (52+ weeks) for standard-size, and from $0.23 to $1.26 for oversize.
Amazon’s own example: 100 units of a standard-size product at 0.05 ft³ each in July costs 100 × 0.05 × $0.78 = $3.90 for the month. The same units in November would cost $12.00.
Aged inventory adds more: items aged 12–15 months pay the greater of $0.30 per unit or $6.90 per ft³ per month, and items over 15 months the greater of $0.35 per unit or $7.90 per ft³. A low-inventory-level fee applies when standard-size and bulky products fall below 28 days of supply.
The takeaway
FBA fees are a function of tier and shipping weight, and dimensional weight sets the shipping weight for everything from Large standard up. Measure the packed product, check its tier, compute the dimensional weight, and see whether a smaller box changes the tier or the weight step before you launch.