StockbeamUnits sold in a typical recent month, divided by 30.
From placing the order to stock on your shelf.
How often you can order. Weekly supplier cut-off: 7. Order any day: 0.
How many days of sales each order should last once it arrives.
The chance of not running out during one reorder cycle.
Optional. Medium is used if you are unsure.
Leave blank to see the order size when you reorder at the reorder point.
- Reorder point
- 171 units
- Suggested order at the reorder point
- 300 units
- Safety stock
- 31 units
How each number is worked out
Demand during the lead time: 140 units
daily sales × lead time. What you expect to sell while the order is on its way.
Safety stock: 30.9 units
z × daily spread × √(lead time + review period). A buffer for sales running above average while you wait. Here z is 1.65 for a 95% service level, the spread is 50% of your daily sales (5 units a day), and the window is 14 days. The review period counts because you cannot fix a shortfall until your next order.
Reorder point: 170.9 units
demand during lead time + safety stock. When your stock, counting anything already on order, falls to this level, place the next order.
Suggested order: 300 units
daily sales × (lead time + days of cover) + safety stock − stock you hold, rounded up. Demand over the window is 440 units. With no stock entered, this assumes you order exactly when you reach the reorder point. Round it up to your supplier’s minimum order or case size.
What this calculator simplifies
The calculator treats your daily sales as a bell curve and assumes the spread is a fixed share of the average, which is why it asks you to choose low, medium or high. The z values are the standard ones for that curve: 1.28 for 90%, 1.65 for 95% and 2.33 for 99%. That is a rough guide. Real sales are often lumpy, with promotions, stockouts and seasons.
Stockbeam does not assume a spread. It measures how wrong its own forecast for each product has actually been, and sizes the buffer from that: a product it predicts well gets little safety stock, and one it predicts badly gets more. Where a product has a seasonal pattern or you have told it about a promotion, it follows that shape across the lead time instead of one flat average. For one product with steady sales, this calculator is a fair first estimate. For a catalogue, treat its answer as a starting point.
Stockbeam does this for every product automatically. See Stockbeam in the Shopify App Store.