If a full reorder-point calculation feels like overkill for your steady sellers, par levels are the simpler cousin. Set a target minimum for each item, and whenever you dip below it, order back up to that number. Restaurants, retailers, and DTC brands use pars to keep shelves stocked without redoing the math on every count.
A par level is a target you top up to. Count stock on a schedule, and if you are below par, order the difference. It is the easiest way to keep steady-usage items in stock.
What "par level" means#
Par level (from "par," meaning the standard or baseline) is the minimum quantity you keep on hand for an item. It does two jobs at once. It acts as a floor, so you never let stock fall below it without reordering, and it acts as a target, so when you reorder you bring stock back up to par.
It is a periodic-review system. You check stock every so often, say weekly, and refill to par, rather than watching for an exact trigger number in real time.
The par level formula#
In plain terms: hold enough to cover demand from now until your next delivery arrives, which is your lead time plus the time until your next stock review, and add a buffer for variability.
A worked example#
A retailer reviews stock weekly and reorders a fast-moving SKU:
- Average usage = 30 units/day
- Lead time = 4 days
- Review period = 7 days (weekly counts)
- Safety stock = 60 units
Then:
Par level = (30 × (4 + 7)) + 60
= (30 × 11) + 60
= 330 + 60
= 390 units
So par is 390 units. At each weekly count, you order enough to bring stock back up to 390. If you are at 120, you order 270.
The classic par mistake is sizing only for lead time and forgetting the review period. If you only count weekly, your par has to carry you through that whole week plus the delivery wait, or you will run dry between counts.
Par level vs. reorder point#
They solve the same problem, which is to not stock out, but they use different mechanics:
| Par level | Reorder point | |
|---|---|---|
| Trigger | Periodic review (e.g. weekly) | Stock hits a set number |
| Order size | Variable, top up to par | Often fixed (e.g. EOQ) |
| Best for | Steady usage, scheduled counts | Continuous tracking, variable demand |
| Buffer | Includes safety stock | Includes safety stock |
Plenty of operations use both: pars for predictable consumables, reorder points for higher-value or more volatile SKUs.
Set and auto-adjust par levels across every product and channel
The bottom line#
A par level is the minimum you keep on hand and the target you refill to. Size it to cover usage across your lead time and your review period, add safety stock, and reset it as demand moves. For steady items it is the lowest-effort way to stay in stock, and Enough Stock keeps those pars current automatically as your run rate changes.