Guide
How much inventory should I order? A simple method for Shopify stores
Stop guessing. Two numbers per product (daily sales and supplier lead time) tell you when to reorder and how much. Worked examples included.
The two questions
Every reorder decision is two questions: when and how much. Both come from the same two numbers per product: how many you sell per day, and how many days your supplier takes.
When to reorder
Example: a candle sells 5 a day and the supplier takes 14 days. Lead-time demand is 70. Add a week of safety stock (35). Reorder when you're down to 105.
How much to order
Same candle, 105 on hand, and you want each order to last 30 days: 5 × (14 + 30) − 105 = 115. If it comes in cases of 24, order 120.
Getting daily sales right
- Use the last 4 weeks, not all-time.
- Exclude days the product was out of stock.
- For seasonal products, compare with the same weeks last year and scale up or down.
Getting lead time right
Lead time is from the day you place the order to the day stock is sellable: supplier production, shipping, customs and receiving. Use what actually happened on your last few orders, not the supplier's quote.
Try it
Plug your numbers into the reorder point calculator, or check how big your buffer should be with the safety stock calculator. For a whole catalog, SteadyShelf runs this for every product every day and drafts the purchase order.
SteadyShelf is launching on the Shopify App Store. Join early access to get the install link first.
FAQ
How do I know when to reorder inventory?
When stock on hand plus stock on order falls to the reorder point: average daily sales x supplier lead time + safety stock.
How much inventory should I order at a time?
Enough to cover the lead time plus the number of days you want the order to last, minus what you already have and have on order, rounded up to the supplier's case pack or minimum.
Should I reorder on a fixed schedule?
A weekly review is a good habit, but the decision for each product should come from its reorder point, not the calendar.
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.
Get early access