Type your monthly sales, supplier lead time and stock on hand. It tells you which products to order, how many, and how many days you have left — for up to 200 products.
No sign-up · 89 KB · Excel 2010 or later, Google Sheets, LibreOffice
| SKU | Product | Lead time | On hand | Avg / day | Safety stock | Reorder point | Days of cover | Status | Order qty |
|---|---|---|---|---|---|---|---|---|---|
| SKU-0031 | Relay switch A | 28 | 0 | 3.00 | 74 | 159 | 0 | Out of stock | 250 |
| SKU-0012 | Fuel filter 10mm | 21 | 146 | 6.90 | 64 | 209 | 21 | Order now | 270 |
| SKU-0156 | Oil drain plug gasket | 10 | 124 | 12.59 | 51 | 177 | 10 | Order now | 450 |
| SKU-0074 | Ball bearing 16mm | 14 | 245 | 10.51 | 76 | 224 | 23 | Order soon | 300 |
| SKU-0122 | Wiper blade 24in | 18 | 123 | 2.95 | 54 | 108 | 42 | Order soon | 84 |
| SKU-0140 | Spark plug, iridium | 25 | 306 | 4.91 | 51 | 174 | 62 | OK | — |
| SKU-0204 | Door handle, rear left | 30 | 14 | 0.00 | 0 | 0 | — | No demand | — |
What it tells you
No macros, no add-ins. Every number is an ordinary formula you can click on and read.
The buffer that covers bad weeks and late suppliers, sized to the service level you pick.
The stock level at which you order. Above it you wait; at or below it you order today.
How long what's on the shelf lasts at your average daily sales.
Out of stock, order now, order soon, OK or no demand — filter the column and you have today's list.
Enough to get back above the line and cover your usual order cycle, raised to the minimum order and rounded to whole packs.
How to use it
SKU, supplier, unit cost, lead time in days, stock on hand and on order. Minimum order and pack size are optional.
Units sold per month, oldest first. Three months works; twelve is better. Most store platforms export this in one click.
Show only “Order now” and “Out of stock”. That's your purchase list, with quantities, for today.
The formula
The calculator uses the standard model planners use — the same one built into the Inventory & Supply Automation Pack. Here it is in full, so you can check it.
d × LT — average daily demand times lead time in days — is what you'll sell while you wait for the order. Safety stock covers the days when you sell more than average, or the supplier takes longer than promised.
d is average daily demand, σd its standard deviation, LT the lead time in days and σLT how many days the lead time varies. If your supplier is reliable, σLT is zero and this becomes the familiar Z × σd × √LT.
The service level is the chance of not running out during one lead time.
| Service level | Z | Good for |
|---|---|---|
| 90% | 1.28 | Cheap, easy-to-replace items |
| 95% | 1.64 | Most products — the default |
| 97.5% | 1.96 | Best sellers |
| 99% | 2.33 | Products you can never be without |
Twelve months of sales average 6.90 a day, with a daily standard deviation of 5.85. The supplier takes 21 days, give or take 4. Service level 95%, so Z = 1.645.
There are 146 on the shelf and none on order, below 209 — so the status is Order now. To get back above the line and cover 30 more days: 209 + 6.90 × 30 − 146 ≈ 270 units.
Questions
Yes. No sign-up, no email, no trial. Use it in your own business and for your clients. The only thing not allowed is reselling or republishing the file itself.
Yes. Upload it to Google Drive and open it with Google Sheets. Every formula works; the only thing that doesn't carry over is the small coloured bars on the Summary tab. It also works in Excel 2010 or later and in LibreOffice.
Three months is enough to start. With fewer months the safety stock is less reliable, so be a little generous with the service level until more history builds up. A month with no sales should be typed as 0, not left blank.
95% suits most products. Use 97.5–99% for best sellers and anything where running out loses you a customer, and 90% for cheap items you can restock quickly. Higher service levels mean more safety stock — more cash tied up on the shelf.
200 rows are ready to use. To add more, copy the last row's grey formulas down on both the Calculator and Sales history tabs.
The calculator tells you what to order when you open it. The Inventory & Supply Automation Pack does it every morning on its own: it reads your Google Sheet, messages you on Telegram, Slack or email before anything runs out, finds dead stock, grades suppliers on their real lead times and drafts the purchase orders.
When you're tired of opening a spreadsheet
Eight n8n workflows that run this calculation every morning, alert you before the shelf is empty, and draft the purchase orders. One-time $79.