In numerology, isopsephy (/ˈaɪsəpˌsɛfi/; from Greek ἴσος (ísos) 'equal' and ψῆφος (psêphos) 'count', lit. 'pebble') or isopsephism is the practice of adding up the number values of the letters in a word to form a single number.[1] The total number is then used as a metaphorical bridge to other words evaluating the equal number,[2] which satisfies isos or "equal" in the term. Ancient Greeks used counting boards for numerical calculation and accounting, with a counter generically called psephos ('pebble'), analogous to the Latin word calculus, from which the English calculate is derived.
Isopsephy is related to gematria: the same practice using the Hebrew alphabet. It is also related to the ancient number systems of many other peoples (for the Arabic alphabet version, see Abjad numerals). A gematria of Latin script languages was also popular in Europe from the Middle Ages to the Renaissance, and its legacy remains an influence in code-breaking and numerology.