Quantity-weighted packaging cost and the next purchase price
When identical packaging arrives in unequal quantities at different unit costs, average the total cost across the total units. Giving each receipt's unit price equal weight can misstate the cost represented by the available stock. Keep that historical average separate from the price used to budget the next purchase.
Normalize the receipts to the same physical unit
T901516PK is clear natural-rubber carton-sealing tape listed at 2 inches by 55 yards, with six rolls per case. For this calculation, use individual rolls as the common unit. Preserve the exact SKU so a different tape grade or roll length is not blended into the same quantity merely because it is also called tape.
Assume two hypothetical receipts remain entirely unused: one six-roll case costing $24 and two six-roll cases costing $60 in total. These amounts are invented examples, not Packrift prices or quotes. Both amounts use the same included-cost basis.
| Receipt | Rolls | Total included cost | Cost per roll |
|---|---|---|---|
| A: one case | 6 | $24 | $4 |
| B: two cases | 12 | $60 | $5 |
| Combined pool | 18 | $84 | About $4.67 |
Weight the prices by quantity
The combined figure is (6 × $4 + 12 × $5) divided by 18, or $84 divided by 18. This applies the weighted-mean formula documented by NIST, with roll quantities as the weights.
The simple average of $4 and $5 is $4.50. Multiplying that figure by eighteen rolls gives $81, which does not reconcile with the $84 total. Equal weighting would be appropriate only if the quantities represented by those two prices were equal.
Use the right figure for the next decision
The approximately $4.67 average describes the defined historical pool. If a new hypothetical quote were $30 for six rolls on the same cost basis, its replacement price would be $5 per roll. Budgeting that purchase from the old average would understate the quoted requirement.
Keep historical purchase records, quantities still available and current quotes in separate fields. If earlier material has been consumed, do not silently treat all historical receipts as the current stock pool. This worksheet is a purchasing comparison, not an instruction to replace the business's accounting method.
Preserve the cost boundary
Review T901516PK's case specification with the actual records. Use the same treatment of included charges across receipts, retain full precision during calculation and round the displayed result afterward. Keep the receipt total and physical-unit total visible so purchasing can reproduce the comparison when another lot arrives.