Roman Numeral Converter

Roman Numeral Converter

Convert between Arabic numbers (1, 2, 3...) and Roman numerals (I, II, III...) instantly. Whether you need to decode a year on a building cornerstone, format an outline, number a list, or simply figure out what MCMLXXXIV means, this converter handles all numbers from 1 to 3,999.

How Roman Numeral Conversion Works

Roman numerals use seven symbols and two rules -- additive and subtractive. The seven symbols are I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000).

Additive rule -- when a symbol of equal or lesser value follows a larger one, add it. VIII = 5 + 1 + 1 + 1 = 8. MDCCC = 1000 + 500 + 100 + 100 + 100 = 1,800.

Subtractive rule -- when a smaller symbol precedes a larger one, subtract it. IV = 5 - 1 = 4. XC = 100 - 10 = 90. Only six subtractive pairs are valid: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900).

Arabic to Roman algorithm -- decompose the number from largest to smallest using a lookup table of 13 values: 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1. For each value, append its symbol as many times as it fits, then move to the next. Example: 1984 = 1000 (M) + 900 (CM) + 80 (LXXX) + 4 (IV) = MCMLXXXIV.

Worked Examples

Example 1 -- Movie copyright year. A film's end credits show "Copyright MCMXCIX." Break it down: M=1000, CM=900, XC=90, IX=9. Total = 1999. The film was copyrighted in 1999.

Example 2 -- Super Bowl number. Super Bowl LVIII is played in 2024. L=50, V=5, III=3... wait -- LVIII = 50 + 5 + 1 + 1 + 1 = 58. The 58th Super Bowl, played in February 2024 between the Kansas City Chiefs and San Francisco 49ers.

Example 3 -- Building cornerstone. A courthouse has "MDCCCLXXXVIII" carved above the entrance. M=1000, D=500, CCC=300, LXXX=80, VIII=8. Total = 1888. The building was constructed in 1888.

Reference Table

Year Reference Table

When to Use

• Decoding years on film credits, building cornerstones, or clock faces where Roman numerals are used decoratively.
• Numbering chapters, volumes, appendices, or outline sections in formal documents and books.
• Understanding Super Bowl, Olympics, and World Cup numbering that uses Roman numerals by convention.
• Reading monarch and pope names (Henry VIII, Pope John Paul II, Elizabeth II) to know the ordinal number.
• Creating properly formatted legal, academic, or organizational outlines where Roman numerals indicate top-level sections.

Common Mistakes

1. Writing four of the same symbol in a row. IIII, XXXX, and CCCC are not valid in standard notation. Use the subtractive forms IV, XL, and CD instead. (Clock faces are an intentional historical exception -- they commonly use IIII for 4.)
2. Using invalid subtractive pairs. Only I, X, and C can be placed before a larger symbol, and only before the next two values in the hierarchy. IL (49) and IC (99) are not valid -- use XLIX and XCIX instead.
3. Reading subtractive pairs out of order. In MCMXCIX (1999), CM and XC and IX are each separate subtractive units. Reading M, C, M, X, C, I, X one symbol at a time gives the wrong result. Always identify subtractive pairs first before summing.
4. Exceeding three consecutive symbols. No symbol repeats more than three times consecutively. MMMM (4000) is not valid -- the standard system tops out at MMMCMXCIX (3999). Numbers above 3999 require a vinculum (overline) notation not covered by standard usage.

Quick Reference Benchmarks

Roman numeral length varies noticeably with number size. The shortest possible Roman numeral is I (1). The longest commonly encountered is MMMCMXCIX (3999) at 9 characters. Years in the range 1800-1899 start with MDCCC (5 characters just for the century), making them among the longest Roman year representations -- MDCCCLXXXVIII (1888) is 13 characters, one of the longest possible values. Years from 2000-2099 start with just MM, making them comparatively compact.

Tips

1. To read an unfamiliar Roman numeral year, group it into M's (thousands), then look for CM or D for the century, then XC or L for the decade, then IX or V for the ones. Work left to right one chunk at a time.
2. MCM = 1900 and MM = 2000 are the two key anchors for modern years. Everything else builds on one of these.
3. The mnemonic "My Dear Cat Loves Extra Vitamins Indeed" maps to M (1000), D (500), C (100), L (50), X (10), V (5), I (1) in descending order.
4. In formal outlines, the standard hierarchy is Roman numerals at the top level (I, II, III), then capital letters (A, B, C), then Arabic numerals (1, 2, 3), then lowercase letters (a, b, c), then lowercase Roman numerals (i, ii, iii).
5. When typing Roman numerals in digital text, always use capital Latin letters (I, V, X, L, C, D, M) -- they are visually distinct and universally recognized, unlike the lookalike Unicode Roman numeral characters.
6. The six subtractive pairs worth memorizing in order: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Knowing these by heart lets you read any Roman numeral without a reference table.