The two fees every FBA seller pays
Amazon charges FBA sellers two separate fees on every sale. The referral fee is Amazon's cut for the sale itself — a percentage of the sell price that varies by category, from around 8% for electronics and beauty to 15% for most general categories and up to 20% for jewelry. It's the same structure whether you fulfill the order yourself or use FBA.
The FBA fulfillment fee is what you pay for Amazon to pick, pack and ship the item, and it's based on size and weight rather than price — a small standard item (under 1 lb) runs around $3.50, while an extra-large or heavy item can run $15 or more. This is why product dimensions matter as much as sourcing cost when picking what to sell: a cheap, lightweight item keeps far more of its margin than an equally cheap but bulky one.
On top of these two per-sale fees, FBA sellers also pay monthly inventory storage fees (higher October–December) and, for most products, some spend on Sponsored Products ads to get initial visibility — both matter for real profitability but are harder to estimate per-unit, which is why this calculator focuses on the two fees you can plan precisely.
Why size tier can matter more than referral rate
Two products at the same $25 price point and 15% referral fee can have wildly different margins purely based on size. A small standard item pays a $3.50 fulfillment fee; the same-priced item in a large bulky tier pays $9.50 — a $6 swing that's often bigger than the entire product cost. Sourcing decisions (packaging size, material weight) that shave a product into a lower size tier frequently do more for margin than negotiating a cheaper unit cost.
This is also why many successful FBA sellers deliberately target the 'sweet spot': products priced $20–$50, weighing under 2–3 lbs, and small enough to qualify for the cheaper fulfillment tiers — a combination that keeps combined referral + fulfillment fees under 30% of the sell price.
Worked example
A $25 item costing $6 to make plus $1 to ship to Amazon, in a standard category (15% referral) at the large-standard size tier: referral fee is $3.75, fulfillment fee is $5.50, total costs are $16.25, leaving $8.75 profit — a 35% margin and a 125% ROI on the $7 you spent to get the unit into Amazon's hands. That's a healthy FBA product; drop the price to $18 with the same costs and margin falls to under 10%, which is why price testing before committing to inventory matters as much as the sourcing decision.