Definition of physical quantities

Physical quantities are often defined in textbooks as measurable quantities. I find this definition confusing. For example, if you think about it, the number of clothes in a cupboard is also a measurable quantity but it is not a known physical quantity in physics. Please give a definition of physical quantities that withstands scrutiny.

• This seems pretty broad and vague. What is a "known physical quantity in physics?" Why should physicists not be allowed to talk about the number of socks in a drawer? – Ben Crowell Apr 27 '18 at 3:35