Inventory how-to

How to set par levels for supplies

A par level is the stock amount that should trigger a reorder.

Short answer: A par level is the stock amount that should trigger a reorder. For supplies, calculate it from how fast you use the item, how long it takes to get more, and a buffer for delays. Set it per item, not as one blanket number for everything.

What a par level actually is

A par level is the minimum quantity you want on hand before you reorder. Below that line, you risk running out before new stock arrives. Above it, you are tying up cash in stock you do not need yet.

For supplies (packaging, labels, boxes, bags, tape, inserts) the logic is the same as for sellable products. You just need to track usage rate instead of sales rate.

The formula

Par level = daily usage x (lead time in days + safety days).

Daily usage is how many units of the supply you go through per day on average. Lead time is how many days it takes your supplier to deliver after you order. Safety days are extra days of buffer for supplier delays or demand spikes. Add the two together and multiply by daily usage to get your par level.

How to find daily usage for supplies

Supplies do not show up in your sales reports, so you need to track them separately. Count how many units of a supply (say, shipping boxes) you used over the last 28 to 60 days, then divide by the number of days. If you ship more around certain weeks (holidays, promotions), use a recent normal period and adjust upward for known busy stretches.

If a supply ties directly to units sold, such as one poly mailer per order, you can estimate usage from order volume instead of counting physical stock.

Reviewing and adjusting

Par levels are not fixed. Review them every few months or whenever your order volume changes significantly. If a supplier's lead time gets longer, or you start running a promotion that increases order volume, raise the par level ahead of time rather than reacting after you run out.

Step by step

  1. List every supply item you reorder regularly (boxes, mailers, tape, labels, inserts).
  2. For each one, count units used over the last 28 to 60 days and divide by days to get daily usage.
  3. Get the lead time from each supplier, in days from order to delivery.
  4. Pick a safety day buffer per supplier, more for unreliable or overseas suppliers.
  5. Calculate par level = daily usage x (lead time + safety days) for each item.
  6. Set a reorder trigger at that par level and check stock against it weekly.
  7. Revisit the numbers whenever volume, suppliers, or lead times change.

Worked example

A store uses 40 shipping boxes a day on average. The box supplier has a 10-day lead time and the store adds 4 safety days for delays. Par level = 40 x (10 + 4) = 560 boxes. Whenever the stock of boxes drops to 560, it is time to reorder, assuming no other boxes are already on order.

How SteadyShelf helps

SteadyShelf forecasts and reorders sellable product variants in your store, not packaging or other non-sellable supplies, since those are not tracked as product sales. For supplies, use the same reorder point formula manually with a spreadsheet or your supplier ordering system, using usage counts instead of sales data.

$29/month flat, unlimited products and suppliers, 30-day free trial. Run the numbers now with the free reorder point calculator.

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FAQ

Can I use the same par level formula for products I sell, not just supplies?

Yes, the formula is the same: daily sales x (lead time + safety days). For sellable products, SteadyShelf calculates this automatically from your sales history and each supplier's lead time, so you do not need to track it by hand.

What if my supply usage varies a lot week to week?

Use a longer tracking window, such as 60 or 90 days, to smooth out the swings, and add more safety days to cover the variability. If usage spikes are predictable, like a seasonal promotion, increase the par level temporarily ahead of that period instead of relying on the average.

Let SteadyShelf do this math for every SKU

Order-by dates per supplier, seasonal forecasts and draft POs for your Shopify store. $29/month after a 30-day free trial.

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