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Weeks of Supply Calculator

Weeks of stock cover at the current sales rate, to help time reorders.

Result

4.53

How it is calculated

The tool divides the stock you have by the amount you sell or use per week: weeks of supply = inventory ÷ weekly sales. Inventory and weekly sales must use the same unit (units, cases, kilograms), and inventory cannot be negative. Weekly sales must be above zero, because dividing by zero is meaningless, so there is no result for a product that did not sell. The answer is a number of weeks shown to two decimals; the 0.53 in 4.53 is a fraction of a week, not a number of days. It assumes demand stays flat at the rate you entered. Seasonality, promotions, incoming orders and supplier lead time are not part of the calculation.

Worked example

A shop holds 1,450 units of an item and sells an average of 320 units per week. Weeks of supply = 1,450 ÷ 320 = 4.53 weeks. Multiply by 7 to see about 31.7 days of cover. If the supplier takes 6 weeks to deliver, 4.53 weeks of stock is not enough, so the order should have been placed already; with a 3-week lead time you would still have roughly 1.5 weeks to spare.

Try this example →

Common mistakes

  • Mixing units, for example inventory in cartons and sales in single items. Both numbers must be counted the same way.
  • Using one unusually strong or weak week as the weekly sales. A longer average gives a steadier figure.
  • Entering monthly or daily sales in the weekly field. Daily sales must be multiplied by 7 and monthly sales divided by about 4.3 first.
  • Reading 4.53 as 4 weeks and 53 days. The decimal is a fraction of a week; 0.53 of a week is about 3.7 days.
  • Ignoring lead time and open orders. Weeks of supply says how long stock lasts, not when you must reorder.

About this calculator

Weeks of Supply measures how long current inventory will last at the current rate of usage, calculated as Weeks of Supply = Inventory on hand / Average weekly usage (or demand). A result of 6 means the stock on hand would cover six more weeks of sales or consumption if nothing were reordered.

Supply chain planners, retail buyers and inventory managers track this figure to decide when to reorder stock, flag slow-moving items sitting on shelves too long, or spot products at risk of running out — it is one of the standard metrics used alongside inventory turnover to balance stockout risk against excess holding costs.

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