A small requirement change can add an entire purchase pack.
Why is a cost range wider than a proportional quantity range?
Use the matching calculator
Use this decision sequence
- Use lower and upper quantity bounds on the same usable-unit basis.
- Round each endpoint to whole compatible packs separately.
- Apply the corresponding supplied price bounds after rounding.
- Show the pack-count jump rather than smoothing the order into a continuous quantity.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Continuous quantity | Changes gradually. |
| Whole-pack quantity | Changes at discrete thresholds. |
| Quoted bound | A stated scenario endpoint, not a forecast probability. |
Worked comparison
An illustrative need ranging from nine to eleven usable units crosses a ten-unit pack threshold. At supplied pack prices of $20–$25 and $5 delivery, the lower bound is one pack at $20 plus $5 = $25, while the upper is two packs at $25 plus $5 = $55. A two-unit requirement difference therefore produces a much larger purchase-cost range.
Check before using the estimate
The bounds are entered worst-case scenarios, not market predictions or recommended contingencies.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.
Related decisions
Keep enough precision before converting volume to bags
Can rounding a displayed volume change the whole-bag count?
Rebase only the cost portion tied to a supplied index
Why can applying an index ratio to the full estimate overstate an adjustment?
Price whole purchase packs
Why does multiplying exact need by a unit price understate a store purchase?
Compare complete supplier baskets
Why can the cheapest quote on each item fail to give the cheapest delivered basket?