THE REFERENCE SHELF
Quantity & value
Milliliters and grams are different purchase units
A cream’s texture does not supply a density for converting mass into volume.
A conditioner bar needs a mass-based comparison
A solid format should not inherit a liquid bottle’s volume or promised use count.
Keep the selected bottle size with the price
A product family can offer several sizes at different amounts.
Compare price within a clearly named use category
A leave-in spray and a rinse-out bottle can have different directions and purchase scope.
Three official US bottles,with their printed volumes
Keep price,size and actual use category together.