A cheaper pack is not necessarily cheaper for the same quantity. When commissioning a refill catalogue, agree the measurement unit, pack quantity and reference amount before displaying a unit price. Keep the payable pack price visible so a customer does not mistake a per-unit comparison for the amount charged.
Who should use this acceptance brief
Refill, consumables and wholesale-pack retailers. Use this as a scoped commissioning task for a website supplier. Where system evidence is required, a teaching file is not a substitute.
Source-bound platform fact
Shopify documents a total quantity and reference measure for unit pricing, with theme/display support to check. Regional legal obligations require separate qualified review. Shopify: unit pricing · Checked 16 October 2026.
Filled teaching example
Synthetic example, not a client case. Inputs, expected decisions and counterexamples follow; no live platform integration is claimed.
On narrow screens, scroll to read the complete table.
| Input / case | Check basis | Expected decision |
|---|---|---|
| AUD12 | AUD per litre | AUD16.00/L |
| AUD18 | same basis | AUD12.00/L |
| AUD10 | invalid quantity | reject |
Run the acceptance exercise
- Approve the pack price, total physical quantity and reference quantity from product records.
- Convert compatible units explicitly; never compare mass and volume without product-specific evidence.
- Inspect card, detail and checkout displays with the same pack and a boundary-rounding example.
Interpret the result and retain evidence
The teaching calculation is pack price in cents × reference millilitres ÷ pack millilitres. The larger pack wins this finite comparison, but does not prove a better purchase for a customer who cannot use it. Keep decimal rounding as a documented display step and retain the unrounded calculation for diagnosis.
Limits before implementation
No statutory unit-pricing compliance claim, currency conversion, density conversion or actual supplier price comparison. All amounts are synthetic.
Replay the finite example
Save both files in one folder and run with Node22.13 or newer. These finite checks are not a live service or certification. Filled inputs and expected outputs · Inspectable functions
node decision-check.mjs pack-unit-price-comparison.json