Roman Numeral Converter

Roman numerals use seven symbols: I (1), V (5), X (10), L (50), C (100), D (500) and M (1,000). When a smaller numeral appears before a larger one, it is subtracted (e.g. IV = 4, IX = 9). Otherwise, values are added left to right.

This converter translates between standard Arabic numbers and Roman numerals for values from 1 to 3,999. Roman numerals are still used in the UK for clock faces, film credits, monarchs (Charles III), chapter numbering and dates on cornerstones.

Roman numerals — the basics. I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Numbers formed by combinations: II = 2, III = 3, IV = 4 (one less than 5), VI = 6, IX = 9 (one less than 10), XL = 40, XC = 90, CD = 400, CM = 900. Subtractive principle: I before V or X subtracts; X before L or C subtracts; C before D or M subtracts. Sample: MCMXCIX = 1000 + 900 + 90 + 9 = 1999.

Common Roman numerals to recognise. Years: MCM = 1900, MCMLXXXIV = 1984, MM = 2000, MMXX = 2020, MMXXVI = 2026. Roman clocks: I, II, III, IIII (often used instead of IV for symmetry), V, VI, VII, VIII, IX, X, XI, XII. UK monarch numbers: Elizabeth II, Charles III, Henry VIII, George VI. Popes: Pope John Paul II (JP2), Francis (no number). Movie sequels: Rocky II, Rambo III, Toy Story IV. Super Bowl: LVIII = 58, LIX = 59 (2025).

UK uses of Roman numerals. Book chapters: Chapter VII, etc. Outline format: I. A. 1. a. i. Roman numerals II often used for sub-points. Royal Society publications. Page numbering for prefaces (i, ii, iii). Tombstone dates. Building cornerstones (MMCC = 2200). Olympic Games: XXX Olympiad 2012. Clock faces (Big Ben, Westminster). Watchmaking — classical clock face style. Movie copyright years.

Limitations of Roman system. No zero — concept didn't exist in Roman mathematics. No standardised representation for numbers >3,999 (variants: V̄ for 5,000 with overline; or use M, MM up to ~3,999). No fractions in standard form (Romans used unciae — twelfths). Arithmetic difficult — Roman system poor for calculation. Replaced by Hindu-Arabic numerals (0-9) for math from ~13th century. Roman only ceremonial/decorative use today.

Quick conversion tips. Decimal → Roman: greedy algorithm — repeatedly subtract largest possible Roman value. 2026: 2000 = MM; 20 = XX; 6 = VI; total MMXXVI. Sample 1492 (Columbus): 1000 (M) + 400 (CD) + 90 (XC) + 2 (II) = MCDXCII. Roman → Decimal: sum values; if smaller before larger, subtract. MCMXCIV = M(1000) − C(100) + M(1000) − X(10) + C(100) − I(1) + V(5) = 1994. Mental shortcut: read left-to-right, each lower-then-higher pair = subtract; lower-then-lower = add.