The reorder quantity formula
The right reorder quantity covers your expected sales during the time it takes to receive new stock, plus a buffer in case demand spikes or delivery is delayed. The formula is:
Where:
Daily Velocity = units sold per day (based on recent sales history)
Lead Time = days from order to delivery
Safety Stock = buffer days you want to keep on hand
Forecast Days = how many days ahead you want to plan
Current Stock = units you have on hand right now
If the result is negative, you have more stock than you need for the forecast period and don't need to reorder yet. If you have a minimum order quantity (MOQ) from your supplier, round up to that.
Free reorder quantity calculator
Reorder Quantity Calculator
Enter your numbers below to calculate how much to order.
Understanding each variable
Daily velocity
This is how fast you're selling a product. Calculate it by dividing total units sold by the number of days in your measurement period. Use at least 30 days of data for accuracy, 60-90 days is better for products with variable demand.
Lead time
The number of days between placing a purchase order and having stock available to sell. Include transit time, receiving, and any processing time. If your supplier says "2-3 weeks," use 21 days to be safe.
Safety stock
A buffer to protect against unexpected demand spikes or delivery delays. A common starting point is 7 days of sales. If your product has highly variable demand or your supplier is unreliable, increase this.
Forecast period
How far out you want to plan. 90 days is a common default — it gives you enough runway to avoid multiple reorder cycles while not over-committing capital.
Minimum order quantity (MOQ)
Your supplier's minimum. If your calculated reorder quantity is less than the MOQ, you have to order the MOQ anyway. Factor this into your safety stock planning.
The problem with doing this manually
The calculation above works great for one product. If you have 50, 100, or 500 SKUs, doing this in a spreadsheet for every product every month is a significant time investment — and spreadsheets go stale the moment you close them.
Stockwise automates this for every product in your Shopify store. It reads your order history, calculates velocity per SKU, applies your lead time and MOQ settings, and shows you exactly what to reorder and when — updated every time you open the dashboard.
Automate this for every product in your store
Stockwise runs this calculation for every SKU automatically, using your actual Shopify sales data. Install free and you'll have your full reorder report in 5 minutes.
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