What the factor-label method does
Dimensional analysis rewrites a quantity by multiplying it by one or more ratios that are equal to 1 in physical meaning, even though they use different unit labels. If the factors are arranged correctly, unwanted units cancel and the desired unit survives.
That makes the method useful for one-step and multi-step conversions alike, especially when a problem moves across prefixes, customary units, or several linked relationships.
starting quantity × conversion factor(s) = target quantity
Core factor-label structure for chained conversions.
2 mi × (5280 ft / 1 mi) = 10,560 ft
Example of unit cancellation leaving only the target unit.