ROMAN NUMERAL
Roman numerals, both ways.
Type 2024 to get MMXXIV, type MMXXIV to get 2024. Range 1–3999 (beyond that needs overline notation). Invalid spellings are explained precisely: IIX and VX are not accepted.
Everything runs locally in your browser
How to use
Pick a direction and type: on the Arabic side an integer from 1 to 3999, on the Roman side any case (lowercase is converted to uppercase). Below the result you get a thousands / hundreds / tens / ones breakdown to help you remember M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, I.
Common questions
Why is there a subtractive form like IV?
Ancient Roman numerals were purely additive: IIII for 4, VIIII for 9. Later, writing a smaller symbol before a larger one to mean subtraction became standard, so 4 became IV and 9 became IX. Only six subtractive pairs exist (IV, IX, XL, XC, CD, CM) and they cannot be mixed freely — 8 is VIII, never IIX.
Why is the limit 3999?
M means 1000 and at most three M may be written, so the largest plain form is 3000. Larger numbers need overlines (a bar over a letter multiplies it by a thousand): 4000 is written as M with a bar. This tool covers the standard forms, hence 1–3999.
How are years written?
Years are commonly written in Roman numerals: 2024 is MMXXIV. Read it digit group by digit group — MM (two thousand), XX (twenty), IV (four) — for 2024. Note it is not read letter by letter: IV is four, not "one, four".
Is any data uploaded?
No. All converting runs locally in the browser.
示例与注意事项Example & notes
一个例子A worked example
把 2024 转成罗马数字得 MMXXIV；反过来输入 MMXXIV 得 2024。若输入 IIX 这类不合规则的写法，会明确告诉你错在「必须按从大到小排列」。2024 becomes MMXXIV, and typing MMXXIV gives 2024 back. A malformed value such as IIX is rejected with the reason spelled out ("symbols must go from largest to smallest").
注意事项Things to watch
- 范围限定 1–3999，更大的数需要字母上横线记法（如 4000 写作 M 加横线）。The range is 1–3999; larger numbers need overline notation (4000 is an M with a bar).
- 减法组合只有 IV IX XL XC CD CM 六种，工具会把其他组合（如 VX、IC）单独拦下并说明。Only six subtractive pairs exist (IV IX XL XC CD CM); anything else (VX, IC) is caught and explained separately.
- 罗马数字侧不区分大小写，输入小写会自动转成大写再解析。The Roman side is case-insensitive; lowercase input is converted before parsing.
相关问答More Q&A
为什么 4 写成 IV 而不是 IIII？Why is 4 written IV rather than IIII?
古罗马原本只有相加写法（IIII 表示 4、VIIII 表示 9）。后来出现「小的写在大的左边表示相减」的规则，4 写成 IV、9 写成 IX，逐步成为标准写法。Ancient Roman numerals were purely additive (IIII for 4, VIIII for 9). A later convention — a smaller symbol before a larger one meaning subtraction — produced IV and IX and became standard.
年份该怎么读？How are Roman years read?
按千位、百位、十位、个位分段读：MM（两千）XX（二十）IV（四）合起来是 2024。注意不是逐字母拼读，IV 读作四而不是「一、四」。Read it group by group — thousands, hundreds, tens, ones: MM (two thousand) XX (twenty) IV (four) makes 2024. Not letter by letter: IV is four, not "one, four".