Tolvido Roman Numerals Converter

Roman Numerals Converter – Numbers to Roman Numerals and Back

Convert numbers to Roman numerals and back as you type, from 1 to 3999, with a step-by-step breakdown and clear reasons why IIII or IC is wrong.

Step by step

    Type in either field and the other updates as you type. Works from 1 to 3999, in upper or lower case.

    Roman numeral symbols

    Symbol IVXLCDM
    Value 1510501005001000

    Subtractive pairs

    Symbol IVIXXLXCCDCM
    Value 494090400900

    Type a number to get its Roman numeral, or type a Roman numeral to read its value: the other field updates as you type. The converter shows how the result is built, symbol by symbol, and when a numeral isn't valid (IIII, VX, IC) it tells you which rule it breaks and what the standard form is. It covers 1 to 3999, accepts lower case, and runs entirely in your browser.

    How it works

    Roman numerals use seven symbols: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. A number is written from the largest value to the smallest and the values are added up: XVI is 10 + 5 + 1 = 16, and MDCLXVI uses each symbol once to make 1666. To avoid four identical symbols in a row, six combinations use subtraction: a smaller symbol placed before a larger one is taken away from it. IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. Only I, X and C are ever subtracted, each only from the next two symbols up (I from V and X, X from L and C, C from D and M), and only one at a time. V, L and D are never repeated and never subtracted. To convert a number, the tool takes the largest value from the list M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, I that still fits, writes it down, subtracts it and repeats until nothing is left. Converting back, it reads the numeral from left to right, subtracting a symbol when the next one is larger and adding it otherwise, then checks that writing the result out again gives exactly what you typed. That check is what catches numerals that add up to something but aren't written the standard way, such as IIX or VV. The largest number in standard notation is 3999, MMMCMXCIX, since M can only be repeated three times. There is no zero, and there are no negative numbers or fractions.

    Worked example

    The year 1994 splits into thousands, hundreds, tens and units: 1000 + 900 + 90 + 4. Each part has its own symbol: 1000 = M, 900 = CM (100 before 1000), 90 = XC (10 before 100) and 4 = IV (1 before 5). Put together: 1994 = M + CM + XC + IV = MCMXCIV. The other way round, MMXXVI reads as M + M + X + X + V + I = 1000 + 1000 + 10 + 10 + 5 + 1 = 2026. A common mistake is writing 99 as IC. I may only be subtracted from V and X, so 99 has to be built from 90 + 9: XC + IX = XCIX. In the same way 49 is XLIX, not IL, and 1999 is MCMXCIX, not MIM.

    Frequently asked questions

    How do you write 2026 in Roman numerals?

    2026 is MMXXVI: MM for 2000, XX for 20 and VI for 6. 2025 was MMXXV and 2027 is MMXXVII.

    Why is there no zero in Roman numerals?

    The Roman system counts things rather than marking place values, so it never needed a symbol for nothing. Zero as a digit reached Europe with Hindu-Arabic numerals in the Middle Ages; medieval scholars who needed it in tables wrote the word nulla or the letter N instead.

    What is the largest number you can write in Roman numerals?

    In standard notation, 3999 (MMMCMXCIX), because no symbol may appear more than three times in a row. For larger numbers the Romans drew a bar (a vinculum) over a numeral to multiply it by 1000, so V̄ meant 5000 and X̄ 10,000, but that bar isn't part of the standard form used today.

    Why do clocks show IIII instead of IV?

    Most clock and watch faces with Roman numerals use IIII for 4, the so-called watchmaker's four. The usual explanations are that it balances the heavy VIII on the opposite side and that the Romans themselves often wrote IIII. Some famous clocks, such as Big Ben's dials in London, use IV. Everywhere else, IV is the standard form.

    Are IIII or IC ever correct?

    Ancient inscriptions do have additive forms like IIII and VIIII, and irregular ones like XIIX for 18, because the rules weren't fixed until much later. Today's standard is the strict subtractive one, and that's what this converter checks: it flags IIII, IC or VX and offers the standard form (IV, XCIX, V).

    Does it matter if I type in lower case?

    No. Lower-case numerals (mcmxciv) are read the same way; they are common for book prefaces and list items (i, ii, iii). The result is always written in capitals.

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