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About this tool
Convert numbers to Roman numerals and back with strict validation, place-value breakdowns, and symbol references.
The Roman Numeral Converter turns any whole number from 1 to 3999 into a Roman numeral and back, using strict standard notation — only the six subtractive pairs IV, IX, XL, XC, CD and CM are accepted, I/X/C/M may repeat at most three times, and V, L and D never repeat. Both fields convert live in either direction, and a place-value breakdown splits the number into thousands, hundreds, tens and units so you can see how the symbols were assembled. When a numeral is rejected it explains exactly which rule broke, rather than just showing an error.
Open Roman Numeral Converter on AltFTool — it loads instantly in your browser.
Type a value into Number (1 – 3999), or type a numeral such as MMXXIV into the Roman numeral field.
Both fields convert live in either direction; an invalid numeral names the rule it breaks instead of showing a bare error.
Read the Place-value breakdown splitting the number into thousands, hundreds, tens and units, and press Copy on either field.
Rejects VX, IIII or DD with the specific rule broken — repeated V/L/D, four repeats, or a subtraction that is not one of the six allowed pairs.
Shows 2024 as MM + XX + IV with each place labelled, so the construction of the numeral is visible rather than memorised.
Typing digits fills the numeral and typing a numeral fills the digits, with year presets for quick checks.
In standard notation the highest is 3999, written MMMCMXCIX, which is the upper limit this converter accepts. M (1000) may repeat at most three times, so 4000 and above need overline notation — a bar above a symbol multiplying it by 1000 — which is not part of the standard set.
Because I, X, C and M can repeat at most three times in a row, so 4 is written IV — one subtracted from five. IIII does appear on some clock faces as a traditional exception, but it fails standard validation and the converter flags it.
Exactly six: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). Any other smaller-before-larger combination, such as IL for 49 or VX for 5, is invalid; 49 is XLIX. Everything outside these pairs must run largest to smallest, left to right.
2024 is MMXXIV — MM for 2000, XX for 20 and IV for 4. Break the year into place values, convert each separately, then join them from largest to smallest; that is exactly the breakdown the converter displays.
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