Inventory glossary

What is Weeks of supply?

Weeks of supply is the number of weeks your current stock will last at the rate you are selling it.

For a small Shopify store, weeks of supply tells you how much breathing room you have before a SKU runs out. It is easier to act on than a raw unit count because it accounts for how fast the item actually sells.

Use it to decide what to reorder now and what can wait. A SKU with two weeks of supply needs attention today, while one with twelve weeks does not, even if the unit counts look similar on a shelf.

Formula

Weeks of supply = Units on hand / Average weekly sales

Example

A candle store has 180 units of a scented jar candle in stock. Over the last four weeks it sold 60 units, so average weekly sales is 15 units. Weeks of supply is 180 / 15 = 12 weeks.

Common mistakes

  • Using total sales instead of average weekly sales, which inflates or deflates the number.
  • Ignoring seasonality, so a spike or dip in recent weeks skews the average and gives a misleading figure.
  • Forgetting to subtract committed inventory, like units already allocated to unfulfilled orders.

Weeks of supply and SteadyShelf

SteadyShelf tracks weeks of supply per variant and uses it with each supplier's lead time to tell you the order-by date before a SKU runs out.

Work it out for your own products with our free tool: Days of stock calculator.

SteadyShelf is launching on the Shopify App Store. Join early access to get the install link first.

Related terms

Days of supply · Average daily sales · Reorder point · Stock cover · Safety stock

Full inventory glossary

FAQ

Is weeks of supply the same as days of supply?

They measure the same idea on different time scales. Days of supply divides units on hand by average daily sales, while weeks of supply divides by average weekly sales. Multiply weeks of supply by 7 to get days of supply.

What is a good number of weeks of supply to hold?

There is no fixed number that fits every store. It depends on your supplier's lead time, how much the item's sales fluctuate, and how costly a stockout would be for that product, so compare your weeks of supply against your lead time rather than a generic target.

Let SteadyShelf do this math for every SKU

Order-by dates per supplier, seasonal forecasts and draft POs for your Shopify store. $29/month after a 30-day free trial.

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