It depends on what you consider to be "customary" and what you wish to convert them to.
Chat with our AI personalities
If you don't know their equivalence, then you can either get a common denominator, and compare the numerators. Or you can divide and convert them all to decimal form and then compare.
You can convert units of length to units of length, and units of area to units of area. But it doesn't make sense to convert between units of length and units of area.
It doesn't make sense to convert that. You can convert units of length to units of length, for example; but you can't convert a pure number to a length.
It doesn't make sense to convert that. You can only convert units of the same kind, e.g., units of length to units of length; units of area to units of area; units of time to units of time, etc.
You can't convert that. You can only convert units that measure the same type of thing - for example, units of length to units of length, units of mass to units of mass, units of time to units of time, etc.