From what I know, a preposition "per" is commonly used for the units of measurement containing fractions. For example, kilogram/liter [kg/L] can be safely pronounced as "kilogram per liter"; but can you also use the following spoken variants that one would use for the numerical fractions, such as:
- kilogram by liter;
- kilogram over liter;
- kilogram into liter,
or anything else? Or is
X per Y the only correct form in this case?