Guide: spares
How to set a reorder point for maintenance spares
A reorder point is the stock level at which you buy more, early enough that the parts arrive before you run out. For maintenance spares it is usage during the supplier's lead time, plus a buffer for the breakdown that cannot wait. This page is that arithmetic in plant language. It is not a purchasing system.
Key takeaways
- Reorder point = usage during the lead time + a buffer you can explain.
- Lead time is how long the part really takes to arrive, not how long the catalogue says.
- Critical spares are the ones whose stockout stops production or creates a safety risk. They earn a buffer. Dead stock does not.
- A suggestion from software is a starting number. A manager still sets the point.
- If issues are not recorded against jobs, the usage figure is a guess.
The reorder point, in one line
Use the same units all the way through. If usage is pieces per week, lead time is in weeks.
Reorder point = (average usage per period x lead time) + buffer- Average usage
- How many you issued over a period you trust, divided by the length of that period. A year is better than a quiet month.
- Lead time
- From the day you decide to buy until the part is on the shelf and fit to use. Include approval, the supplier, transport and inspection.
- Buffer
- Extra stock for a demand spike or a late supplier. For a critical spare this may be one full replacement. For a cheap consumable it may be a few days of use.
This is the plain form plants can do on paper. It is not a claim about the exact formula inside any one software product.
A worked example
Worked example (illustrative)
A plant uses about 8 mechanical seals of one size in a year, so roughly 0.15 a week. The supplier takes 6 weeks, and last year one order took 10. The seal fits three critical pumps, and a stockout stops a line.
Usage during a 6-week lead time is about 0.9 seals. The team sets the buffer at 2, because one failure during a late delivery should still leave a seal, and they do not want to round a critical spare down to zero. Reorder point = 0.9 + 2, which they round to 3. They reorder 4, about half a year of use, so they are not raising a purchase every month. All of these numbers are illustrative.
The expensive mistake is the opposite one: 20 seals on the shelf because someone once waited, and 18 of them will still be there in five years. That is dead stock. Count it, and stop reordering it.
Critical spare, ordinary spare, dead stock
Sort the crib before you calculate anything. A critical spare is a part whose absence stops production, breaks a safety control, or cannot be borrowed from another machine. Hold the buffer. An ordinary spare is a filter or a belt you use steadily. The formula above is enough. Dead stock has not moved for a period you choose, often a year, and is not critical. Do not reorder it. Use it, return it, or write it off.
Usage only means something if every issue is written against a job or a machine. A bin that "feels low" is how the same seal is both out of stock and overstocked, depending on who you ask.
Worked checks before you trust the number
Look at the last five issues of the part. If they are missing, the average usage is a story, not a figure. Look at the last three purchase arrivals and write the real lead time, including the week the indent sat for approval. Then ask what happened the last time the bin was empty: did the line stop, or did someone borrow a seal from another pump?
Recalculate twice a year, and after any change of supplier. A reorder point from 2022, left in a cell, is how you hold stock for a machine you scrapped. Critical spares still deserve a named owner. A formula will not notice that the only person who knows the supersession left the plant.
Keep the calculation on the part record in plain language: usage, lead time, buffer, and the date you set it. The next storekeeper should not have to reverse-engineer why the minimum is 3. If two machines use the same part number but one is critical and one is not, the buffer follows the critical use. Do not average them into a number that protects neither. Review the point when the supplier or the machine changes, not only on a date nobody opens. A minimum that has sat unchanged for two years is a guess that got lucky, or a guess that is about to stop a line. Write the reason for the buffer in the same place as the number, so the next person can defend it.
Where MaintenanceIQ fits
MaintenanceIQ records receipts, issues and adjustments, and it ties parts used to the work order. Spares optimization shows days of cover, stockout risk, overstock and dead stock from that usage, and it suggests a reorder point for a manager to review and set. It does not raise a purchase order, and it does not connect to an ERP. Parts move in and out by the transactions your team records, and by CSV.
See spare parts inventory and spares optimization.
Sources
- Operations & Maintenance Best Practices Guide, Release 3.0 (opens in a new tab), U.S. Department of Energy, Federal Energy Management Program
Frequently asked questions
What is a reorder point?
The stock level at which you place the next order, set so the new parts arrive before you run out. It is usage during the lead time, plus a buffer.
How do I set the buffer?
From the consequence of running out, and from how late the supplier has actually been. A critical seal can justify a buffer of one or two. A cheap filter used every week needs only a few days of cover.
Does MaintenanceIQ order the parts for us?
No. It suggests a reorder point from your usage. A manager reviews it and sets it. Purchasing stays in your purchasing process.
What if we have no usage history?
Start with the OEM recommended spare and the lead time you were last quoted, mark the part critical or not, and review the point after three months of real issues. Do not pretend a year of history you do not have.