You need 2 things to begin with:
1) a unit of length: mm, cm, m, in, ft, miles, and so on.
2) what figure do you need to use to convert.
For example: 1 Centimetre = 0.39370 Inches
0.39370 x 5 = 1.9685 inches in 5 centimetres
It depends on what you consider to be "customary" and what you wish to convert them to.
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.
It depends on what you consider to be "customary" and what you wish to convert them to.
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 use conversion factors.
Some customary units of length include inches, feet, yards, and miles in the United States. In other countries, units like centimeters, meters, and kilometers are common for measuring length.
metric
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.
10 1/2
You can't compare units of mass with units of length.
It doesn't make sense to convert units that measure completely different things. You can only convert units of length to units of length, units of mass to units of mass, 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.