Aequicalculus

Aequicalculus (a Latin translation of the Greek isopsephy, ἴσος, isos ["equal"] + ψῆφος, psephos ["pebble"]) is a system of converting Latin letters to defined numeric values, based on Greek-to-Latin correspondences, as observed by John Opsopaus. Unlike in Greek isopsephy or Hebrew gematria, where the conversions are based on classical utilisation of every glyph as both a letter and a numeral, Latin only utilised a limited set of letters in combinations as ordinary numbers (I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000), and consequently the conversions are not based on routine equivalencies but rather assumed correspondences with other languages.

Tools

 * https://hatch.kookscience.com/cipher/iso.php?cipher=la_3