Dimensional analysis
Tons and kilometres cannot be converted. They measure different physical properties.
To convert from one metric unit to another, use conversion factors. Multiply the value you are converting by the appropriate conversion factor to get the desired unit. For example, to convert meters to centimeters, multiply by 100 since there are 100 centimeters in one meter.
Newtons are a measure of force, joules are a measure of energy. The two measure different characteristics and, according to the most basic rules of dimensional analyses, attempting to convert from one to the other is not valid.
It is impossible to convert the measure of weight (mass) to the measure of length (distance). Forget the not necessary word "linear".
It means that you have a measurement in one unit (for example, 10 km), and convert it into the equivalent in some other unit (for example, 10,000 meters).
You don't really "convert a unit of measurement"; you convert from one unit to another. The two - "from" and "to" are always required.
That means that if you have a measurement in one unit, you convert it to another unit. For example, if a measurement is given in millimeters, you may need to convert it to meters.
move the decimal point the the correct spot
You can't convert milliliters to meters. You can convert one unit of volume to another (for example, milliliters to liters, or to cubic meters), one unit of length to another (for example, millimeter to meter), but you can't convert units that measure completely different things.
There isn't any one general answer. It depends on what unit you want to convert to what other unit.
You can't convert that. In general, you can only convert from one unit to another of the same kind, for example, one unit of mass to another unit of mass.
You can't convert that. You can convert from one linear unit to another linear unit, or from one square unit to another square unit, but not between linear units and square units.
You can't convert that. You can convert from one linear unit to another linear unit, or from one square unit to another square unit, but not between linear units and square units.
You can't convert that. You can convert from one unit of length to another, or from one unit of area to another, but you can't convert between units of length and area.
You can't. Miles is a measure of length. Acres is a measure of area.
If you mean, convert µg to cm², that conversion doesn't make sense. You can only convert units that measure the same kind of thing, for example, one unit of mass to another unit of mass.
By dividing the multiple by the root unit.