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Roman Numeral Converter
Convert whole numbers to Roman numerals and canonical Roman numerals back to numbers with live validation and a value-by-value breakdown.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Two-way conversion
Whole numbers from 1 to 3,999
Standard subtractive notation
Result
MMXXVI
2,026 = MMXXVI
Value breakdown
left to right1000 + 1000 + 10 + 10 + 5 + 1 = 2,026
How it works
- Enter a whole number or type a Roman numeral using I, V, X, L, C, D, and M.
- The other representation updates live and strict notation errors are explained.
- Use the breakdown to see additive and subtractive values, then copy the result.
FAQ
What number range is supported?
The converter handles standard modern Roman numerals from 1 through 3,999 (I through MMMCMXCIX). Larger values usually require overline conventions that are not represented consistently in plain text.
Why is IIII rejected?
The converter validates canonical modern notation, where 4 is written IV. It similarly expects IX, XL, XC, CD, and CM for the standard subtractive pairs.
Is zero represented in Roman numerals?
Classical Roman numerals do not have a standard zero symbol, so this converter begins at 1.
Can I convert in both directions?
Yes. Edit either the Arabic-number field or the Roman-numeral field; the opposite side and the value breakdown update immediately in your browser.
Roman numeral rules at a glance
Largest first
Symbols normally descend in value from left to right and their values are added.
Subtraction
A smaller permitted symbol before a larger one forms values such as IV or XC.
Repetition
I, X, C, and M may repeat up to three times in standard modern notation.