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In this guide
The bill of materials tells you what goes into one kit. It does not tell you how many of each part to buy. Order exactly 5,000 of every component for a 5,000-kit at-home testing build and the build will usually come up short. The part that runs out is rarely the cheap one. It is the printed carton or the custom label with a four-week reprint.
Where the units go between the PO and the shipped kit
Every component passes through several points where units leave the count. None of them is a mistake. Each is a normal part of receiving, building and inspecting a regulated kit, and each has an owner who can tell you the number in advance.
| Loss point | What happens | Where the number comes from |
|---|---|---|
| Printer overs and unders | Printing trade customs let a printer deliver up to 10 percent more or fewer than ordered, billed on what arrives, unless you set a tolerance at quote | Your print quote |
| Receiving | Cases that arrive crushed, wet or outside specification are rejected at the dock | Supplier packaging and the receiving procedure |
| First article and setup | The first units built are checked against the approved sample and the work instruction before the line runs | The work instruction |
| Sampling | Final inspection pulls a sample sized by the sampling plan. Some checks consume the unit | The agreed sampling plan |
| In-process damage | Torn labels, misregistered prints, dropped tubes, a pouch seal that fails | Build history on similar kits |
| Dating | Components that will expire before the program ends cannot be built into later lots | Component expiry dates |
The printed component is usually the one that runs short
Printers run to a quantity, not a count. Setup sheets, makeready and trimming waste mean the press cannot land exactly on your number, so the trade custom gives the printer room in both directions. A common written form is that overruns or underruns will not exceed 10 percent of the quantity ordered, and that a buyer who needs a guaranteed quantity must say so when the job is quoted.
Read that from the kit side. Order 5,000 folding cartons and a delivery of 4,550 is within tolerance. You pay for 4,550, you can build 4,550 kits, and the next 450 wait on a reprint. If the carton is the only component with a long lead, the whole program waits on it.
Two fixes work. State an under tolerance of zero (overs only) when you request the quote, and expect the unit price to reflect it. Or size the order so the worst allowed under still covers the build. Our guide to what a packaging printer needs from you covers the files; the quantity terms belong on the same request.
Sampling only costs units when the check is destructive
Under the ISO 2859-1 and ANSI/ASQ Z1.4 tables at general inspection level II, a 5,000-unit lot draws a sample of 200. The sample size is set by lot size and inspection level, and the acceptance number by the AQL. Our post on AQL and sampling plans explains how those pieces fit.
What matters for ordering is whether the sample comes back. A visual check of a sealed, labeled kit usually returns the unit to stock. Opening a sterile swab pouch, uncapping a prefilled tube or pulling a seal to test it does not. Ask which checks in your plan are destructive and add those units per lot, not per program. A program built in four lots pays that cost four times.
A worked example
Illustrative example. A 5,000-kit build with three components that behave differently. Your figures come from your quotes, your sampling plan and your supplier pack sizes.
| Component | What drives the overage | Order |
|---|---|---|
| Printed folding carton | Allowed under of 10 percent: 5,000 divided by 0.9 is 5,556, plus a small allowance for setup and handling | About 5,650 |
| Sterile swab, cases of 100 | No print tolerance. Eight units opened for a destructive check per lot, plus 1 percent handling damage: 5,058 | 5,100 (51 cases) |
| Specimen label, rolls of 1,000 | About 20 labels lost threading each roll. Five rolls give 4,900 usable labels | 6 rolls |
Notice that the label line is driven by pack size and the swab line by case count. A single overage percentage across the BOM would overbuy the swab and still leave you short on labels.
Overage is not waste if you plan where it goes
Leftover components have three good uses. They carry into the next build when their dating allows; our post on why a kit expires when its shortest-dated component does covers that check. They become replacement kits for at-home testing participants whose kit arrived damaged or who made a collection error, a pool every direct-to-consumer or decentralized program needs anyway. And they cover retained samples if your quality agreement calls for them.
Decide the replacement pool size up front. If you expect a share of participants to need a second kit, that share belongs in the build quantity, not in a rush order three weeks after launch.
Settle these before the purchase order
- Which components have a print tolerance, and did the quote state over and under limits?
- Which inspection checks consume the unit, and how many units per lot?
- What are the case pack, roll and minimum order quantities for each part?
- How many lots will the program run in?
- What replacement kit rate will you plan for?
- Will leftover components still be in date for the next build?
Bring the answers to the BOM review. The quantity per kit and the quantity per program are two different calculations, and only the second one ships.
Sources: University of Wisconsin Digital Publishing and Printing Services, printing policies and trade customs (over runs and under runs). How the AQL inspection levels in ISO 2859-1 affect sample size. ANSI/ASQ Z1.4, Sampling Procedures and Tables for Inspection by Attributes.
