Stockouts on critical spares turn routine PMs into extended downtime. Enter how fast you use a part, how long your supplier takes, and the buffer you want — and get the exact stock level that should trigger a reorder.
Your reorder point
6 units
When stock hits 6, reorder — you'll receive parts before you run out even if usage spikes.
RunTight tracks stock and fires reorder alerts automatically — free for teams up to 25.
A reorder point answers one question: at what stock level do I need to order so the replacement arrives before I run out? The formula has two parts. Lead-time demand is what you'll consume while waiting on the supplier — daily usage multiplied by lead time in days. Safety stock is the buffer on top, expressed here as extra days of cover — daily usage multiplied by the number of buffer days. Add them together:
Reorder point = (daily usage × lead time) + (daily usage × safety stock days)
The calculator rounds up to the next whole unit, because you can't stock 0.4 of a bearing and rounding down defeats the purpose of the buffer.
Say you go through about 2 of a particular bearing per week — roughly 0.29 per day — and your supplier takes 14 days to deliver. Lead-time demand is 0.29 × 14 ≈ 4 bearings: that's what you'll consume between placing the order and receiving it. Add a week of safety stock (0.29 × 7 ≈ 2 bearings) and the total is 6. So the reorder point is 6: when the shelf drops to 6 bearings, order. You'll burn through roughly 4 while the order is in transit and still have about 2 in reserve if a machine eats an extra bearing or the truck shows up late.
Safety stock is a judgment call, but three factors should drive it. Usage variability: a part consumed at a steady, predictable rate needs only a few days of cover, while one that gets used in unpredictable bursts — failure-driven replacements rather than scheduled ones — deserves a week or more. Criticality: if a stockout takes down a production line, carry more; if the part only feeds a convenience repair, carry less and accept the occasional wait. Supplier reliability: a vendor that ships on time, every time, needs little buffer, but one whose “14 days” sometimes means 21 should have that gap baked into your safety days. For a deeper look at organizing your storeroom around these decisions, see our guide to maintenance parts inventory management.
Ignoring lead time changes. Reorder points are set once and then the supplier changes, freight slows down, or a distributor stops stocking the part locally — and the number that used to leave a comfortable buffer now guarantees a stockout. When lead time moves, the reorder point has to move with it.
Using the same safety stock for every part. A blanket “one week of cover” policy overstocks cheap, steady consumables and understocks the erratic, critical spares that actually cause downtime. Set safety days per part, or at least per class of part.
Never revisiting the numbers. Usage rates drift as equipment ages, gets rebuilt, or gets retired. A reorder point calculated from last year's consumption can be badly wrong today. Recheck your fast movers quarterly and everything else at least once a year — or use software that watches actual consumption for you. If you're still tracking parts on paper or spreadsheets, our free maintenance templates are a good starting point for getting a parts list under control.
A reorder point is the stock level that triggers a new purchase order. It's calculated so that the parts you have left cover your usage during the supplier's lead time, plus a safety buffer — meaning the replacement order arrives before the shelf goes empty. When on-hand quantity drops to the reorder point, you order; you don't wait for zero.
The simplest method — the one this calculator uses — is extra days of cover: multiply your daily usage by the number of days of buffer you want. Pick more days for parts with erratic usage, critical equipment, or unreliable suppliers, and fewer days for steady consumables from dependable vendors. Statistical methods using demand standard deviation exist, but days-of-cover is accurate enough for most maintenance storerooms and far easier to maintain.
Use the longest lead time you regularly see, not the average, or add the difference into your safety stock days. If a supplier quotes 14 days but occasionally takes 21, calculating with 14 days will leave you short exactly when it matters. Revisit the number whenever you change suppliers or notice deliveries slipping.
RunTight is free for up to 25 users — including parts inventory tracking and automatic reorder alerts. Pro adds advanced analytics and the REST API for $49/month.
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