Roman Numerals Converter, Chart and Symbols

The seven symbols and where they came from

Roman numerals are built from seven letters and nothing else. I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1,000. There is no zero, no decimal point and no way to write a negative number.

The shapes are older than the letters they borrowed. I began as a single notch on a tally stick and X as the tenth notch, cut across. V is the top half of that X, or a hand with the thumb out. C and M were later matched to the Latin words centum and mille, which is a neat memory aid even though the symbols did not start out as abbreviations. D is the right half of an older symbol for 1,000.

Read a numeral by adding the values left to right, largest first: MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1, which is 2026. The only wrinkle is the subtractive pairs, covered next.

• I = 1
• V = 5
• X = 10
• L = 50
• C = 100
• D = 500
• M = 1,000

The subtractive rule: why 4 is IV and not IIII

When a smaller numeral is written in front of a larger one, you subtract it instead of adding it. IV is 5 minus 1, which is 4. IX is 10 minus 1, which is 9. That keeps numerals short and stops long runs of repeated letters.

The rule is tightly limited. Only I, X and C are ever subtracted, and each may only be taken from the next two larger symbols. That gives exactly six valid pairs: IV, IX, XL, XC, CD and CM. V, L and D are never subtracted, because they are already half-steps, so VX and LC are not numerals at all.

Two mistakes follow from ignoring this. 49 is XLIX (40 + 9) and not IL, because I can only be subtracted from V or X. 99 is XCIX (90 + 9) and not IC. The same logic makes 1999 MCMXCIX rather than the tempting MIM.

• IV = 4 and IX = 9, subtracting I from V and X.
• XL = 40 and XC = 90, subtracting X from L and C.
• CD = 400 and CM = 900, subtracting C from D and M.
• Never repeat a letter more than three times in the standard modern form.
• The Romans themselves were looser. IIII and XXXX appear on real inscriptions, and the tidy rules we teach were settled long after Rome fell.

How to write any number in Roman numerals

Split the number into thousands, hundreds, tens and units, convert each part on its own, then write the parts side by side in that order. The pieces never interfere with each other, which is what makes the method reliable.

Take 1987. The thousands give 1000, which is M. The hundreds give 900, which is CM. The tens give 80, which is LXXX. The units give 7, which is VII. Put them together and you have MCMLXXXVII.

Take 449. There are no thousands. 400 is CD, 40 is XL and 9 is IX, so 449 is CDXLIX. Reading back the other way uses one rule: scan left to right, and if a symbol is smaller than the symbol to its right, subtract it, otherwise add it.

• Thousands: 1000 M, 2000 MM, 3000 MMM.
• Hundreds: 100 C, 200 CC, 300 CCC, 400 CD, 500 D, 600 DC, 700 DCC, 800 DCCC, 900 CM.
• Tens: 10 X, 20 XX, 30 XXX, 40 XL, 50 L, 60 LX, 70 LXX, 80 LXXX, 90 XC.
• Units: 1 I, 2 II, 3 III, 4 IV, 5 V, 6 VI, 7 VII, 8 VIII, 9 IX.

Numbers above 3,999 and the overline

With plain letters the system runs out at 3,999, written MMMCMXCIX. Going further would need four Ms in a row, which the standard form does not allow, and that is why most online converters simply refuse anything larger.

The classical answer is the vinculum, a bar drawn over a numeral to multiply it by 1,000. V with a bar is 5,000, X with a bar is 10,000, and M with a bar is 1,000,000. So 25,000 is X̄X̄V̄ and 4,000 is IV̄ or MMMM depending on which convention you follow.

Typing the bar is awkward. There is no single character for a barred V: you type the letter and follow it with the combining macron U+0304 or the combining overline U+0305, and the result depends on the font. On the web, wrapping the numeral in a span with text-decoration overline is far more dependable. Romans before the vinculum used the apostrophus instead, writing CIƆ for 1,000 and IƆ for 500, and Unicode preserves those as ↀ, ↁ and ↂ.

Why clock faces show IIII instead of IV

Look at almost any traditional clock or watch dial and the four is IIII, not IV. This is not an error, it is a centuries-old convention in horology, and it predates the strict subtractive rule becoming standard.

The most convincing explanation is visual balance. IIII sits directly opposite VIII, so the bottom half of the dial carries similar visual weight on both sides, while a light IV opposite a heavy VIII looks lopsided. A practical argument backs it up: a dial's numerals could be cast in identical batches, twenty Is, four Vs and four Xs, filling four moulds exactly with no leftovers.

Other explanations are less solid. The story that Louis XIV insisted on IIII is charming and unproven, and the idea that IV was avoided because it begins the name IVPITTER is folklore. Big Ben uses IV, which settles the matter: this is a design convention and not a rule of the numeral system.

Roman numerals for dates and tattoos

A date is just three numbers converted separately and joined with a separator. 7 June 1998 becomes VII . VI . MCMXCVIII. Choose your order deliberately, because day-month-year and month-day-year both appear and the numerals give no clue which you meant. A dot, a middle dot or a small gap all read well, while a slash tends to crowd the letters.

If it is going on skin, check it three times and then check it in a different font. The most common errors are writing 1999 as MIM, 40 as XXXX, 9 as VIIII, and simply mistyping the year. Have the artist copy your text rather than retype it, and see the stencil on your arm before the needle comes out.

Elsewhere, Roman numerals survive in monarch and pope names (Elizabeth II, Benedict XVI), Super Bowls (LIX is 59), film sequels and the copyright year buried in the end credits, chapter numbers and preface pages, the Olympiads, chemistry oxidation states such as iron(III), and chord numbering in music theory.