Start with a correction, because the version of this story doing the rounds is wrong.
You’ll have read that Amazon “extended dimensional weight to all major size tiers in 2026.” It didn’t. Amazon extended dimensional weight to large standard-size products below 12 ounces in 2022, and to apparel from 16 February 2023. Under the tier definitions in force right up to 14 January 2026, Amazon already used dimensional weight for Large standard, oversize, Large Bulky and Extra-Large whenever it exceeded unit weight. Nothing about that is new.
What actually changed on 15 January 2026 is more specific, and more expensive for a particular set of SKUs:
- The Large Bulky tier split, creating a new Small Bulky tier
- A new packaging fee on bulky units not enrolled in SIPP, priced by dimensional weight
- A new Overmax handling fee of $17–$25 on very large items
- The low-inventory-level fee and inbound placement fees now reach bulky products
- A 3.5% fuel and logistics surcharge on top of fulfilment fees from 17 April 2026
If your product is bulky, this is the year your fees moved. If it’s standard-size, you’re mostly looking at rate adjustments and an average increase of about $0.08 per unit sold — Amazon’s own figure, which it frames as under 0.5% of an average item’s price.
One thing to establish before going further: this is the US story. There is no equivalent UK or EU size-tier change for 2026. European fees went the other way — referral fees were cut in several categories, and FBA parcel fees fell by around £0.26 on average. Don’t transplant the American numbers onto UK SKUs.
How dimensional weight actually works
Dimensional weight in pounds = (length × width × height in inches) ÷ 139.
Amazon bills on shipping weight, which is the greater of unit weight and dimensional weight. That same comparison also determines which size tier you land in.
Where it applies: Large standard, Small Bulky, Large Bulky, and Extra-Large up to 150 lb. Where it doesn’t: Small standard and Extra-Large over 150 lb, both of which use unit weight only.
There’s a trap in the detail. For Small Bulky, Large Bulky, Overmax and Extra-Large items, Amazon assumes a 2-inch minimum on width and height, regardless of how flat the product actually is. Amazon’s own worked example makes the point better than any explanation:
A white dry erase board, 40 × 1 × 25 inches, unit weight 4.5 lb. Dimensional weight is calculated as 40 × 2 × 25 ÷ 139 = 14.4 lb, because the 1-inch depth is rounded up to the 2-inch minimum. In 2025 it was Large Bulky. In 2026 it is Small Bulky.
A 4.5 lb board billed as 14.4 lb. Flat products get no reward for being flat once they’re in a bulky tier.
The effect on standard-size items is just as real. Amazon’s example of a t-shirt at 13 × 9 × 0.85 inches: unit weight 5.4 oz, dimensional weight 1.65 lb. It’s billed in the 1.5–1.75 lb band, at $6.14 non-peak. A 5.4-ounce shirt paying a 1.75-pound fee.
UK sellers, note the different divisor. European FBA uses (L × W × H in cm) ÷ 5,000, in force since 1 March 2023, applying to oversize products excluding special oversize, and to small and standard parcels, with a long list of exempt categories including Footwear, Clothing, Grocery, Mattresses, Home Linen and Pet Food, which are billed on unit weight only.
The 2026 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 (new) | ≤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 lb | ≤50 lb | beyond Large Bulky limits | |||
| Overmax (new) | Extra-Large to 150 lb exceeding 96 in longest side or 130 in length + girth |
Girth is 2 × (median side + shortest side). Everything that is Small Bulky today was Large Bulky in 2025.
The bulky packaging fee — the change that matters
Here’s the mechanic worth understanding, because it isn’t a rate rise, it’s a restructure.
Previously, SIPP-enrolled bulky products got a flat $1.32 per unit discount. That discount is gone. In its place, Amazon cut base bulky fulfilment rates and introduced a packaging fee on bulky units that are not SIPP-enrolled, priced by dimensional weight:
| Dimensional weight | Packaging fee | Dimensional weight | Packaging fee | |
|---|---|---|---|---|
| 0–5 lb | $1.51 | 25–30 lb | $3.47 | |
| 5–10 lb | $1.68 | 30–35 lb | $3.60 | |
| 10–15 lb | $1.97 | 35–40 lb | $3.78 | |
| 15–20 lb | $2.60 | 40–45 lb | $3.80 | |
| 20–25 lb | $2.92 | 45+ lb | $4.04 |
Amazon says it averages $2.07 per unit. Note it’s priced on dimensional weight, not shipping weight — Amazon’s reasoning being that dimensions determine the packaging required.
SIPP: Ships In Product Packaging — means the unit ships in its own packaging with no Amazon overbox. Certified products up to 20 lb qualify. You enrol at the SIPP enrolment page, supply a first arrival date, and discounts apply only to units received after that date.
Who won and who lost — Amazon’s own numbers
These are Amazon’s published comparisons, not estimates:
Small Bulky, SIPP enrolled — vent cover filter (18 × 17.75 × 2.75 in) 2025: $11.63 fulfilment − $1.32 SIPP = $10.31 → 2026: $9.57. Saves $0.74.
Small Bulky, not SIPP — baby cot (24 × 7.5 × 6 in) 2025: $12.27 → 2026: $10.21 + $1.97 packaging = $12.18. Roughly flat.
Large Bulky, SIPP enrolled — shoe storage bench (47.5 × 17.25 × 4.38 in) 2025: $19.03 − $1.32 = $17.71 → 2026: $18.77. Costs $1.06 more.
Large Bulky, not SIPP — book shelf (37.58 × 12.27 × 5.74 in) 2025: $20.74 → 2026: $20.48 + $2.60 packaging = $23.08. Costs $2.34 more.
Overmax — bulletin board (96 × 48 × 7 in) 2025: $33.55 → 2026: $33.55 + $17.00 Overmax handling fee = $50.55. Up 51%.
The pattern: products that dropped from Large Bulky into the new Small Bulky tier came out ahead. Products that stayed Large Bulky paid more, whether or not they were SIPP-enrolled. And anything crossing 96 inches on its longest side picked up a fee that adds half again to its fulfilment cost.
Three other fees that widened in 2026
Low-inventory-level fee. Charged per unit shipped when both your trailing-90-day and trailing-30-day historical days of supply fall below 28 days, with the tier set by the greater of the two. From 15 January it measures at FNSKU level rather than parent-ASIN level, Grocery became exempt, and it now applies to Small and Large Bulky. Exemptions still cover new Professional sellers for 365 days, new-to-FBA parent products for 180 days, SKUs where 70%+ of inventory arrived via AWD auto-replenishment, and anything selling fewer than 20 units in the past 7 days.
Aged inventory surcharge. Changed 16 January 2026, one day after everything else. A new 456+ day tier was added at $7.90 per cubic foot or $0.35 per unit, whichever is greater, and the 366–455 day per-unit rate doubled from $0.15 to $0.30. Snapshot is taken on the 15th of each month, charged between the 18th and 22nd, with removal orders needing to be in by 11:59pm PT on the 14th to avoid it.
Inbound placement service fee. Now applies to Small and Large Bulky. New weight bands were added between 3 and 20 lb. Amazon’s own example: a 6 lb Large standard item, 100 units, one East-region location on minimal splits, moved from $0.37 to $0.42 per unit — $5 more on a hundred units, but multiply it across a year of inbound. The Amazon-optimized shipment splits option remains free, including on bulky, if you can ship five or more identical cartons per item.
And from 17 April 2026, a 3.5% fuel and logistics surcharge applies on top of fulfilment fees for FBA in the US and Canada, extending to Buy with Prime and Multi-Channel Fulfillment on 2 May.
What to do about it
Pull the Fee Preview report and check the tier column. The report carries longest-side, median-side, shortest-side, item-weight and product-size-tier — the exact figures Amazon bills against. Anything sitting in Small Bulky or Large Bulky needs looking at this week.
For every bulky SKU, work out whether SIPP pays. The maths is now simple: if the packaging fee for your dimensional weight band exceeds the cost of making the product SIPP-certified, enrol. At $1.51 to $4.04 a unit, that’s usually a fast decision.
Find the SKUs sitting just over a tier boundary. Small Bulky caps at 37 inches longest side, 28 median, 20 shortest, 130 length plus girth. Large standard caps at 18 × 14 × 8 and 20 lb. If a product misses a boundary by an inch, redesigning the carton moves it into a cheaper tier permanently. Remember the 2-inch minimum on width and height in the bulky tiers — shaving depth below 2 inches buys you nothing there.
Check the 96-inch line. Overmax is the single most punitive change of the year. Anything approaching 96 inches on its longest side, or 130 inches length plus girth, is worth re-engineering.
Re-run break-even ACoS afterwards. A $2.34 fee increase on a $40 product takes roughly six points off your break-even ACoS. Campaigns that were profitable in December may not be now, and nothing in Seller Central will tell you.
FAQ
What is Amazon’s dimensional weight formula? In the US, (length × width × height in inches) ÷ 139. In the UK and EU, (L × W × H in cm) ÷ 5,000. Amazon bills on the greater of dimensional weight and unit weight.
Did Amazon add dimensional weight to new size tiers in 2026? No. Dimensional weight has applied to Large standard since 2022 and to apparel since February 2023. The 2026 changes are the Small Bulky tier split, a new bulky packaging fee, the Overmax handling fee, and wider application of the low-inventory-level and inbound placement fees.
What is the Overmax handling fee? A fee introduced 15 January 2026 for Extra-Large items up to 150 lb that exceed 96 inches on the longest side or 130 inches length plus girth. It’s $17 for 0–50 lb, $21 for 50–70 lb and $25 for 70–150 lb, charged on top of the fulfilment fee.
Is SIPP still worth it in 2026? For standard-size products the discount continues, at $0.04–$0.23 per unit. For bulky products the $1.32 discount was replaced by a packaging fee of $1.51–$4.04 on units that are not SIPP-enrolled, so the incentive is now larger, not smaller.
Do the 2026 FBA changes apply in the UK? No. There is no equivalent UK or EU size-tier change for 2026. European referral and FBA fees were reduced in December 2025 and January 2026.
Sami Sultan runs Ecom Enable, an Amazon growth partner for DTC brands. All figures verified against Amazon Seller Central on 27 August 2026. Rate cards change annually in mid-January and peak rates apply from 15 October — check the live schedule before modelling.
Sources: Amazon Seller Central 2026 US referral and FBA fee changes, FBA fulfilment fees, product size tiers, dimensional weight, SIPP, low-inventory-level fee, aged inventory surcharge, inbound placement fee; UK/EU dimensional weight; 2026 European fee update.
