stoichiometry

noun

1. the determination of the proportions in which chemical elements combine or are produced and the weight relations in any chemical reaction
2. the branch of chemistry dealing with the relationships of elements entering into and resulting from combination, esp. with quantitative relationships

Origin: < Gr stoicheion, a first principle, element, base, akin to steichein, to step, go (for IE base see stile) + -metry