Nominal size
A nominal size is the round figure a product is sold and named by, such as the 60cm in a 60cm fridge freezer, rather than its exact measurement.
What it means
A nominal size names a size class and does not measure anything. A 60cm fridge freezer is sold, searched for and named as 60cm, though its measured width may be 595 mm. Both figures are true, and they answer different questions.
Trouble starts when they share a column. One row says 60cm, the next says 595, and a filter offers both for what is one real width. Converting the 60cm to 600 mm is worse: it looks exact, yet it is 5 mm out.
Keep them apart. If shoppers filter by nominal size, give it an attribute of its own, and put the measured width in the width field, in millimetres, like every other width in the category. Google’s product dimension attributes are for “the measurements of the product that you’re selling”.1
Think of it like this
Dress sizes work the same way. A size 12 names a range of fits and measures nothing, and the tape measure still decides whether it fits.
For example
An illustrative fridge freezer arrives with Width “60cm” in one column and “595” in a column headed Width (mm). The title keeps the nominal size, “Brackmore 60cm fridge freezer, stainless steel”, and the width field holds 595 mm.
Why it matters
Shoppers search by the nominal size but buy on the measured one, because the appliance has to fit the gap. An AI assistant asked for a fridge freezer that fits an alcove needs the width and height as facts it can compare, and a nominal size cannot supply them.
Not to be confused with
A nominal size is not one of the product dimensions. It is the name a product is sold by; product dimensions are measured, and belong in the width, height and depth fields.