What is SKU velocity and why does it matter?
SKU velocity is the average units sold per day for a specific SKU, usually measured over a rolling 30-day window. It drives every downstream inventory decision: PO size, safety stock, days of cover targets, and IPI score. A SKU whose velocity drops 30% for two weeks is either losing search rank or facing seasonality.
How to measure it
Use a 30-day rolling window for stable SKUs. Use 14 days for launches or seasonal SKUs. Exclude days with stockouts to avoid biasing the average downward.
Why 30% is the alert threshold
Small daily variation is normal. A sustained 30% drop over 14 days almost always signals a real issue: lost keyword rank, a new competitor, a price change, or seasonality. It is worth investigating within the week.
How velocity feeds decisions
PO size = velocity x lead time x safety factor. Days of cover = current inventory / velocity. Restock alerts fire at velocity x reorder-lead-time.
Frequently asked questions
Should I use 30-day or 90-day velocity?
30-day for planning, 90-day for benchmarking. 90-day misses recent trend changes.
How does velocity relate to sell-through?
Sell-through is a 90-day inventory turn ratio. Velocity is a daily unit rate. Both matter but for different decisions.
What causes velocity to drop?
Lost search rank, competitor launches, price increases, listing suppression, review score dropping below 4.0, or seasonality.
Does Nova track SKU velocity?
Yes. Nova shows daily and 30-day velocity per SKU in inventory monitoring.
See this in Nova
Nova surfaces this metric per SKU in near real time so you can act before your next monthly close catches it.
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How do I forecast Amazon demand accurately?
The most accurate simple forecast weights the last 30 days at 60% and the prior 60 days at 40%, then adjusts for seasonality and known promotions. For most private-label SKUs this beats gut-feel and matches what statistical models produce within a 10% margin. Rebuild the forecast every 2 to 4 weeks.
What is days of cover and how do I calculate it?
Days of cover = current on-hand inventory / average daily units sold. If you have 600 units on hand and sell 20/day, you have 30 days of cover. Most sellers target 45 to 75 days of cover for FBA SKUs: enough to survive a demand spike or a shipping delay, not so much that IPI or storage fees suffer.
What is a good sell-through rate on Amazon?
Amazon's sell-through rate is units shipped in the last 90 days divided by average inventory over the same period. Above 3.0 is strong (inventory turns 12x/year). 2.0 to 3.0 is healthy. Below 1.0 usually means overordered units and forecasts long-term storage fees within a quarter.
Why is my Buy Box percentage dropping?
Buy Box share drops for four reasons: a competitor undercut your price by more than 2%, your FBA in-stock rate slipped, seller performance metrics (late shipment, cancellation, defect) crossed a threshold, or Amazon added its own retail offer. Fixing the first three usually restores share within 24 to 72 hours.
How is the Amazon IPI score calculated?
Amazon's Inventory Performance Index (IPI) is a rolling score from 0 to 1000 built from four inputs: excess inventory percentage, sell-through rate, stranded inventory percentage, and in-stock rate on FBA. Scores above 400 keep storage limits open; scores below 400 trigger restock limits and higher storage costs.