Weeks of Supply in Ecommerce Inventory Operations

Weeks of supply measures how long current inventory will last based on expected weekly demand. In ecommerce operations, it converts inventory quantities into a time-based view that makes risk and coverage easier to understand.

Weeks of supply is also referred to as weeks-of-supply or inventory coverage; this article uses “weeks of supply” consistently.

Weeks of supply expresses inventory levels in terms of time rather than units. It answers the question: if sales continue as expected, how many weeks will inventory last?

This metric provides an intuitive way to assess both stockout risk and excess inventory. Low weeks of supply signal imminent risk, while high weeks of supply indicate capital tied up longer than necessary.

In ecommerce, weeks of supply is especially useful because sales velocity can change quickly due to promotions, seasonality, or marketplace dynamics.

Weeks of supply is widely used by ecommerce brands and aggregators to monitor inventory health.

Shopify-based teams use it to align purchasing cadence with sales velocity and campaign timing.

Amazon and Walmart 3P sellers rely on weeks of supply to manage fulfillment inventory coverage and avoid listing downtime.

Multichannel ecommerce teams use weeks of supply to compare inventory risk across channels, locations, and SKUs.

Weeks of supply is calculated by dividing available inventory (often including inbound stock) by expected average weekly demand.

As demand or inventory changes, weeks of supply updates automatically, making it a dynamic monitoring metric.

Teams review weeks of supply regularly to identify items at risk of stockout or excess and to prioritize replenishment or liquidation actions.

Weeks of supply is often used alongside reorder points, helping teams translate abstract thresholds into time-based urgency.

Inventory turnover is inversely related to weeks of supply; higher coverage generally implies slower turnover.

Sell-through rate improves when weeks of supply aligns with realistic demand rather than inflated inventory positions.

Fill rate declines when weeks of supply drops too low to absorb variability.

Weeks of supply itself is the primary coverage metric that ties inventory to time.

Together, these metrics show whether inventory coverage is intentional or drifting out of control.

Is weeks of supply better than units on hand?
It is more intuitive for risk and timing decisions.

Should inbound inventory be included?
Often yes, when assessing future coverage.

How often should weeks of supply be reviewed?
Weekly for fast-moving SKUs, monthly for slower ones.

Can weeks of supply differ by channel?
Yes, due to different demand rates.

Is weeks of supply a planning or execution metric?
It is mainly a planning and monitoring metric.