Roman Numerals to Numbers – Converter and How to Read Them

Roman numerals are written with seven letters: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1,000. Each letter always has the same value, and you add them up to get the number[1]. There is no letter for zero.

The digits we use every day, often called Arabic numerals, work differently. They are positional: the same 2 means two, twenty or two hundred depending on where it stands, and 0 holds the empty places. Binary works the same way with only two digits, which you can see in the decimal to binary converter. Because Roman letters never change their value, a Roman numeral can get long: 1888 is MDCCCLXXXVIII.

Today you meet them in names of monarchs and popes, such as Elizabeth II or Pope Leo XIV, on clock faces, on building fronts and in the copyright year at the end of film and TV credits[1]. In the United States they also appear after names shared across generations, such as William Howard Taft IV.

Read from left to right and add the letters up. There is one exception: a smaller letter placed right before a larger one is subtracted from it. Modern usage has only six of these pairs: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400 and CM is 900[1].

Take MCMXC. M is 1,000. CM is 1,000 minus 100, which is 900. XC is 90. Together they make 1990.

MMXXVI is simpler because there is no subtractive pair in it: MM is 2,000, XX is 20 and VI is 6, so the year is 2026.

A numeral after a name is read as an ordinal: Elizabeth II is Elizabeth the Second[1]. The converter gives you the plain number, 2, and you add the ordinal ending yourself.

Clock faces with Roman numerals very often show four o'clock as IIII and nine o'clock as IX. The habit goes back to very early clocks such as the Wells Cathedral clock of the late 14th century. It is not universal, though: the clock on Elizabeth Tower at the Palace of Westminster uses IV[1].

Additive forms like IIII, XXXX and CCCC were in use long before clocks and kept appearing for centuries. The two styles could even be mixed in one document or in one numeral[1].

The converter reads these forms the same way as any other numeral: a smaller letter before a larger one is subtracted and the rest is added. Excel's ARABIC function also accepts a non-standard form and reads mxmvii as 1997[3]. So you get a result for IIII, MDCCCCX or IC, and the Standard form line under it shows the modern spelling: IV, MCMX and XCIX. A run of equal letters before a larger one is subtracted as a whole, so the old XIIX used by the 18th Roman legion comes out as 18[1].

A bar over a letter, called a vinculum, multiplies its value by 1,000[1]. V with a bar is 5,000, X with a bar is 10,000 and M with a bar is 1,000,000. Letters without a bar keep their usual value, so X̅V is 10,005.

The bar has to sit over every letter it applies to. If the field holds IV̅, with the bar over the V only, the converter subtracts I from 5,000 and gives 4,999, and the Standard form line shows I̅V̅CMXCIX. Four thousand is I̅V̅, with a bar over both letters.

The field accepts the bar pasted as a combining overline or as a macron, for example from text where someone typed Ī. It reads numbers up to 3,999,999.