n = mass / M or mass = n × M
The fundamental equation n = mass/M converts between the measurable quantity (grams on a balance) and the chemist's counting unit (moles). This conversion is the first and last step in almost every stoichiometric calculation: (1) Convert given mass to moles → (2) Use mole ratio from balanced equation → (3) Convert answer back to desired units. For solutions, moles = Molarity × Volume(L). For gases at STP, moles = Volume(L)/22.414. Accuracy depends on using the correct molar mass — always sum atomic masses from the periodic table for the exact formula. In analytical chemistry, precise mass-mole conversions (using analytical balances reading to 0.0001 g) are critical for quantitative results.