# Units & Conversions ## The International System of Units (SI) ## Dimensional Analysis [Converting Units using Multiple Conversion Factors](https://www.youtube.com/watch?v=LdZ00OFAfaQ) A **unit conversion factor** is a ratio of two equivalent quantities expressed with different measurement units. - $1 \ in = 2.54 \ cm$ - **Ex:** ${2.54 \ cm \over 1 \ in} = {1 \ in \over 2.54 \ cm}$ When using conversion factors, the order of what is in the numerator/denominator does **not** matter, so long as the units cancel out. The conversion factor is just a ratio and the goal is to have the same units cancel out. - **Ex:** ${1 \ kg \over 1000 \ g} * {1 \ g \over 20 \ kg}$ The technique of dimensional analysis just applies this concept of conversion factors to more complex