Roman Numeral Converter
Convert between Roman numerals and Arabic numbers instantly, with step-by-step breakdown. Free, educational, no signup needed.
Roman Numeral Converter Tool
How to Use the Roman Numeral Converter
Enter any number from 1 to 3,999
Type a whole number between 1 and 3,999 into the input field (3,999 and 3 999 are both fine), or type a Roman numeral (using I, V, X, L, C, D, M, or a single character such as Ⅻ) to convert back. The tool auto-detects which direction you need. Roman numerals are read in the strict modern standard form only.
The result appears instantly
Conversion happens on every keystroke — no button to press. Auto-detection handles both directions: type "2026" and get MMXXVI; type "XIV" and get 14.
See the step-by-step breakdown
For Arabic → Roman conversions, each Roman component is shown separately as a coloured chip — for example, 2026 = MM (2000) + XX (20) + VI (6) — so you can understand exactly how the result was built.
Use the quick-select pills
Click any of the common value pills (1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000) to load it instantly and learn the key Roman numeral symbols. Use the Swap button to force a specific conversion direction.
Roman numerals on Roman stones and in the modern standard form
What this converter accepts
The converter writes and reads one form: the strict modern standard form. Each digit of the number is written separately, in thousands, hundreds, tens and units, and a digit of 4 or 9 uses one of six subtractive pairs:
- IV = 4 (I before V: 5 − 1)
- IX = 9 (I before X: 10 − 1)
- XL = 40 (X before L: 50 − 10)
- XC = 90 (X before C: 100 − 10)
- CD = 400 (C before D: 500 − 100)
- CM = 900 (C before M: 1000 − 100)
Mark Pilgrim's book Dive Into Python 3 writes this rule as a single regular expression. Our converter checks a numeral by converting it back and comparing, and over every string of one to six of the seven letters it accepts and refuses exactly what that pattern does. In this form 99 is XCIX, never IC, and M repeats at most three times, so the largest number it can write is 3,999, MMMCMXCIX.
Romans and clockmakers wrote other forms
The strict form is a modern convention, and Roman stonecutters did not keep it. The cenotaph of the centurion Marcus Caelius, who fell in the Varian disaster of AD 9, names his legion as XIIX (CIL XIII 8648; transcription at Livius.org). A centurion's tombstone from Viminacium writes the legion IIII Flavia Felix (EDCS-30200719), and a legionary's tombstone at Mainz writes IIII Macedonica (EDCS-10700435).
Clock dials keep IIII too. When UK Parliament described the restored North Dial of the Elizabeth Tower in March 2019, it said the dial shows 4 as IV "rather than the usual IIII on other clocks". We have not found a primary horological source for why clockmakers chose IIII, so this page does not repeat the explanations told about it.
The converter refuses these forms, because it accepts only the standard one. When a refused numeral reads as a whole number in the older way (IIII, VIIII, XIIX, IIX, MDCCCCX), it tells you that number and its standard form, so XIIX is read as 18 and written XVIII.
Numbers the standard form cannot write
The standard form has no zero, no negative numbers, no fractions and nothing above 3,999. Software that needs more has to choose its own rule. Microsoft Excel's ROMAN function returns the #VALUE! error above 3,999. The Unicode CLDR root number-spelling rules write zero as N and go on past 3,999 with the archaic characters Unicode encodes for large numbers, writing 4,000 as Mↁ. A bar over a numeral to multiply it by a thousand is another later convention; this converter writes none of them.
"For most purposes, it is preferable to compose the Roman numerals from sequences of the appropriate Latin letters."
Unicode's Roman numeral characters and full-width digits
Unicode also has single characters for Roman numerals: Ⅰ to Ⅻ, ⅰ to ⅻ, and Ⅼ Ⅽ Ⅾ Ⅿ in both cases. Its standard says these were encoded "for compatibility with East Asian standards" and, unlike sequences of Latin letters, "remain upright in vertical layout". Each of them decomposes to ordinary letters, so the converter now reads them: type Ⅻ and you get 12. Full-width digits and letters, as typed with a Chinese, Japanese or Korean input method, convert the same way, so ２０２６ gives MMXXVI. The archaic characters ↀ ↁ ↂ Ↄ ↅ ↆ ↇ ↈ have no such decomposition and are refused.
Numbers may be typed with thousands separators, as 3,999 or 3 999. A full stop is read as a decimal point and refused, as is anything that is not a whole number.
Where you still see them
Roman numerals still number monarchs and popes (Henry VIII, Pope John Paul II), film sequels (Rocky II, The Godfather Part II), book chapters, outlines and the front matter of books, and the hours on many clock and watch dials.
Corrections on 19 October 2026
Numbers typed with a comma used to convert wrongly and silently: 3,999 became III and 1,000 became I, because only the digits before the comma were read. A decimal point or trailing letters were cut off the same way. They are now read correctly or refused with a message. The suggestion for a refused numeral such as IIX or XIIX was 2 too high on 399 of the 400 numbers ending in 8 (XIIX was offered as XX); it now gives the older-form reading described above. Unicode numerals and full-width digits used to be refused. The current-year line now follows the calendar instead of a fixed year. We also removed examples and claims we could not support or found to be wrong: a Singapore court citation, a papal name and a Malaysian royal title that were each shown with a Roman numeral their official sources do not use, a school-curriculum claim, Super Bowl history, and explanations for IIII on clocks.
XIIX on a centurion's cenotaph, IV on Westminster's North Dial, N for zero
The cenotaph of Marcus Caelius, a centurion who fell in the Varian disaster of AD 9, writes his legion as XIIX, not XVIII (CIL XIII 8648).
Soldiers' tombstones from Viminacium and Mainz write two Fourth legions as IIII Flavia and IIII Macedonica (EDCS-30200719, EDCS-10700435).
UK Parliament says the Elizabeth Tower's North Dial shows 4 as IV, "rather than the usual IIII on other clocks".
The longest numeral in the standard form is MMMDCCCLXXXVIII (3,888), at 15 letters. No other number from 1 to 3,999 is as long.
Microsoft's ARABIC function page gives MXMVII as an example of 1997, a form a strict standard-form validator such as this one refuses; read the older way it is 1997, written MCMXCVII.
The Unicode CLDR root rules write zero as N and 4,000 as Mↁ, using an archaic numeral character Unicode encodes for 5,000.
Unicode's single-character numerals Ⅰ–Ⅻ, their lowercase forms and Ⅼ Ⅽ Ⅾ Ⅿ were encoded for compatibility with East Asian standards, and stay upright in vertical text.
The year 2026 is MMXXVI: M (1000), M (1000), X (10), X (10), V (5), I (1).
Frequently Asked Questions
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In the strict modern standard form, 3,999, written MMMCMXCIX: M repeats at most three times and there is no letter for 5,000. Larger numbers have been written in other notations — Unicode encodes archaic characters such as ↁ and ↂ, and a bar over a numeral is a later convention for multiplying by a thousand — but this converter covers the standard range of 1 to 3,999.
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IV is the modern standard form: a smaller letter before a larger one is subtracted (5 − 1 = 4), and IV is one of the six subtractive pairs the standard uses (IV, IX, XL, XC, CD, CM). It is not the only form in use. Roman tombstones write IIII for the Fourth legions, and IIII is usual on clock dials.
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IIII is the usual figure on clock dials; UK Parliament, describing the Elizabeth Tower's North Dial in 2019, said that dial shows IV "rather than the usual IIII on other clocks". We have not found a primary horological source that documents why clockmakers chose IIII, so we do not repeat the explanations often given.
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It accepts only the strict modern standard form. XIIX and IIII are older forms found on Roman inscriptions and clock dials, not mistakes. When a refused numeral reads as a whole number in the older way, the converter tells you that number and how the standard form writes it: XIIX is 18 (XVIII), IIII is 4 (IV).
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Enter the year in the converter above; the line under the quick-select buttons shows the current year in Singapore time. As an example, 2026 is MMXXVI: MM = 2000 (two thousands), XX = 20 (two tens), VI = 6 (five plus one).
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Yes. Commas or spaces between groups of three digits are accepted (3,999 or 3 999). A full stop is read as a decimal point and refused, because Roman numerals here are whole numbers. Unicode numeral characters (Ⅻ, ⅻ) and full-width digits and letters (２０２６, ＸＩＶ) are converted to ordinary characters first.
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The Roman numeral for 1,000 is M. In the standard form M repeats up to three times: MM = 2,000, MMM = 3,000, and MMMCMXCIX = 3,999 is the largest.
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When a smaller letter comes immediately before a larger one, the smaller value is subtracted from the larger. The modern standard form uses only six such pairs: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). All other letters are added.
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Not in the standard form, which starts at I, so this converter refuses 0 and negative numbers. Software that needs a zero has to pick one: the Unicode CLDR root rules write it as N.
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Read left to right. For each letter, if its value is less than the next letter's, subtract it; otherwise add it. For example, XIV: X (10), then I is less than V so subtract it, then add V: 10 − 1 + 5 = 14. This converter does it for you and also checks that the numeral is in the standard form.
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