What Is GMROI for Amazon FBA?
GMROI (Gross Margin Return on Inventory) measures how much gross profit you earn for every dollar invested in inventory. It is the single best metric for comparing SKU-level performance because it combines profitability and inventory efficiency into one number. A high-margin slow seller and a low-margin fast seller can both be evaluated on the same scale.
A GMROI of 3.0 means you generate $3 in gross profit for every $1 of average inventory at cost. For FBA sellers, a healthy GMROI target is 2.0 to 4.0+. Below 1.0 means you are earning less gross profit than the cost of your inventory investment, a clear signal to reduce stock or discontinue the SKU.
GMROI is especially useful for FBA portfolio management. When you have limited capital and storage capacity, GMROI tells you which SKUs deserve more investment and which are dragging down your returns. It answers the question: where should my next dollar of inventory go?
GMROI Formula
GMROI = Annual Gross Profit / Average Inventory CostAn equivalent formula that makes the components clearer:
GMROI = Gross Margin % × Inventory TurnoverThis shows that GMROI improves when you either increase margin or turn inventory faster (or both).
| GMROI Range | Interpretation |
|---|---|
| Below 1.0 | Losing money on inventory investment |
| 1.0 - 2.0 | Below average; review pricing or velocity |
| 2.0 - 4.0 | Healthy for most FBA sellers |
| 4.0+ | Excellent; high margin and fast turns |
Worked Example: Comparing Two FBA SKUs
SKU A: $50 ASP, $17.50 landed cost, gross margin 65%. Sells 800 units/year, average inventory 200 units.
Annual gross profit: 800 × ($50 − $17.50) = $26,000. Average inventory cost: 200 × $17.50 = $3,500.
GMROI = $26,000 / $3,500 = 7.4
SKU B: $25 ASP, $13.75 landed cost, gross margin 45%. Sells 2,400 units/year, average inventory 300 units.
Annual gross profit: 2,400 × ($25 − $13.75) = $27,000. Average inventory cost: 300 × $13.75 = $4,125.
GMROI = $27,000 / $4,125 = 6.5
SKU A has a higher GMROI despite lower annual volume because its gross margin is stronger relative to inventory investment. Both SKUs are excellent performers. Now compare to a struggling SKU:
SKU C: $30 ASP, $15 landed cost, gross margin 50%. Sells 200 units/year, average inventory 250 units.
Annual gross profit: 200 × $15 = $3,000. Average inventory cost: 250 × $15 = $3,750.
GMROI = $3,000 / $3,750 = 0.8
SKU C returns less in gross profit than the inventory it ties up. Capital allocated to SKU C would generate far more return if redirected to SKU A or B.
GMROI in the FBA Context
Storage fees punish low GMROI SKUs. SKUs with low turns accumulate monthly storage fees and aged inventory surcharges that further erode margins. A GMROI below 1.5 often drops below 1.0 once you factor in aged surcharges, making the SKU a net cash drain.
Use GMROI for reorder prioritization. When cash is tight, rank SKUs by GMROI and allocate reorder budget top-down. High-GMROI SKUs deserve full replenishment; low-GMROI SKUs get reduced quantities or are placed on hold until velocity improves.
Seasonal GMROI swings. A SKU's GMROI can vary dramatically by quarter. Q4 velocity spikes may push GMROI to 6.0+, while Q1 slowdowns drop it to 1.5. Evaluate GMROI on a trailing 12-month basis to avoid over-reacting to seasonal fluctuations.
Common GMROI Mistakes
Only looking at margin. A 70% gross margin means nothing if the product turns once per year. GMROI = margin × turns, so a 40% margin product turning 8x (GMROI 3.2) outperforms a 70% margin product turning 1.5x (GMROI 1.05). Always evaluate both dimensions.
Calculating with revenue instead of cost. GMROI uses average inventory at cost, not at retail. Using retail values inflates the denominator and understates your GMROI. Use your landed cost per unit × average units on hand.
Ignoring Amazon fees in the analysis. Traditional GMROI uses gross margin. For FBA, consider also calculating a contribution-margin version (sometimes called CMROI) that subtracts Amazon fees. A SKU with 65% gross margin but heavy PPC dependency may have a much lower effective return on inventory than the gross GMROI suggests.
Related Glossary Terms
How many times you sell through average inventory per year.
Read →Revenue minus all variable costs including Amazon fees.
Read →Percentage of inventory sold vs. received over a period.
Read →Direct cost of inventory sold during a period.
Read →Average days to sell through current inventory.
Read →Frequently Asked Questions
What is a good GMROI for Amazon FBA?
A GMROI of 2.0 or higher is considered healthy for FBA sellers. Top performers hit 3.0-5.0 by combining strong margins with fast inventory turns. Below 1.0 means you are earning less gross profit than the cost of your inventory investment, a signal to reduce stock or discontinue the SKU.
How is GMROI different from ROI?
GMROI specifically measures gross profit return on inventory investment. ROI is a broader metric that includes all costs and all capital deployed. GMROI isolates how well your inventory dollars are working, making it better for SKU-level comparison and capital allocation decisions.
Should I use gross margin or contribution margin for FBA GMROI?
Traditional GMROI uses gross margin (revenue minus COGS). For FBA decision-making, substituting contribution margin (which includes Amazon fees) gives a more accurate picture of true inventory profitability. Some sellers call this CMROI. Either formula works as long as you apply it consistently across all SKUs.