Prestidigitation and amount (volume) of material

I posted this question in the comments for the Prestidigitation cantrip on DnD Beyond, but I’m thinking that’s not trafficked frequently.

I’m curious how DMs have interpreted "1 cubic foot" for this cantrip. My take is this is different than, for example, a 5-foot cube (Minor Illusion) in that it only specifies volume, not dimensions. This means I could (conceivably) clean the blood off a (idealized) longsword that is 36" x 1/2" x 3" (at the hilt). Volume of a rectangular-based pyramid is 1/3 * a * b * h (a and b being the sides at the base) so in this case 1/3 * 1/2 * 3 * 36 = 108/6 = 18 cu inches (well within the 1728 cu inches in a cubic foot).

How wrong am I?