Free spare parts reorder point calculator
Get the min and max for each spare part. Free, no signup, your data stays in your browser.
My usage numbers are per
Add a part to see when to reorder it.
How the numbers are worked out
- Used during lead time = usage per day × lead time in days.
- Safety stock = service factor × spread of usage during the lead time. The factor is 2.33 for class A, 1.65 for class B, and 1.28 for class C.
- Reorder point (min) = used during lead time + safety stock, rounded up to a whole part.
- Max = reorder point + one order. One order is your usage for the number of days you set above.
Example. You use 6 heater bands a month, the supplier takes 14 days, and the part is class A. Used during lead time: 6 × 14 ÷ 30 = 2.8. Safety stock: 2.33 × √2.8 = 3.9. Reorder point: 2.8 + 3.9 = 6.7, so reorder at 7. An order that lasts 30 days is 6 parts, so the max is 13.
If you leave the spread empty, the calculator assumes parts fail at random, which is how most spares behave. Then the spread during the lead time is the square root of the usage during the lead time. A month counts as 30 days and a year as 365.
Treat the result as a starting point. Check it against your own history, and add more for a supplier that often delivers late.
Want spare parts tracked by bin and tied to work orders? See vMaint features →
Built by Ender Celik
Common questions
What is a reorder point?
The stock level at which you order more. It covers what you expect to use while the order is on its way, plus safety stock for a bad stretch. In a min/max system it is the min.
How is safety stock calculated?
Safety stock is a service factor times the spread of usage during the lead time. The factor is 2.33 for class A, 1.65 for class B, and 1.28 for class C. If you do not enter a spread, the calculator assumes parts fail at random, so the spread is the square root of the usage during the lead time.
What do classes A, B, and C mean?
They say how much a missing part hurts. Class A stops the line, so the level is set to have the part on the shelf 99% of the time. Class B is important and gets 95%. Class C is routine and gets 90%.
What is the difference between min/max and a reorder point?
They are the same system. The min is the reorder point. The max is the min plus one order, so it is the most you should have on the shelf right after a delivery.
Where is my data stored?
In this browser, on this device. Nothing you type is sent to vMaint. Clearing your browser data erases it, so download the CSV of anything you want to keep.