What property is measured by a ruler?
Physical properties are those set of properties which can be observed or measured without changing the chemical composition of the substance.
Rulers measure length.
See, by the definition of what a physical property is we can say that it can be both observed and measured in a system.
In general, we have different types scales for measuring stuff i.e we have temperature scales (kelvin, Celsius and Fahrenheit)for measuring temperature, we have weighing scales( milligrams, grams,kilograms) for measuring mass and so many other scales for measuring different things.
Now, the ruler we use in our classrooms for geometry is used for measuring lengths. So, length can be considered as a physical property which can be measured using a ruler.