Roman Numeral Converter

Type a whole number from 1 to 3,999,999 and press Convert to Roman, or type a Roman numeral and press Convert to Decimal. From 4,000 up the numeral has bars over its thousands. The Add bar button puts one on the letter before the cursor. The converter reads only standard numerals, spelled the way it writes them itself. IIII, VX and MMMM get a message instead of a number.

Decimal → Roman

Integer (1 to 3,999,999)

Roman → Decimal

Roman Numeral

Add bar puts a bar on the letter before the cursor, for numbers from 4,000 up. You can also type _V for a barred V.

How to use the Roman Numeral Converter

Enter your numbers in the Roman Numeral Converter above.
Press the Convert to Roman or Convert to Decimal button to see the result.
To try other numbers, change any value and press the button again.

The Roman numeral system

I=1, V=5, X=10, L=50, C=100, D=500, M=1000 · · · Smaller before larger subtracts (IV = 4); after, adds (VI = 6) · · · A bar multiplies by 1,000 (V̅ = 5,000)

The converter writes and reads the standard form. No letter appears more than three times in a row, so 4 is IV and not IIII. V, L and D never repeat. Only six pairs subtract: IV, IX, XL, XC, CD and CM. From 4,000 up the thousands are written the same way with a bar over them, and the rest follows without a bar. Older and decorative numerals sometimes break these rules, and the converter turns those spellings down.

Worked example

2026 = MMXXVI (1000 + 1000 + 10 + 10 + 5 + 1). 49 = XLIX (50−10 + 10−1). 1999 = MCMXCIX (1000 + 1000−100 + 100−10 + 10−1). 4,026 = I̅V̅XXVI (4 × 1,000 + 26). 50,000 = L̅.

Frequently asked questions

Is there a Roman numeral for zero?

No. Roman numerals have no symbol for zero, so the converter starts at 1.

How do you write Roman numerals over 3,999?

With a bar, called a vinculum, which multiplies a numeral by 1,000. 4,000 would otherwise need four Ms in a row, so it is I̅V̅, and 5,000 is V̅. Plain Roman numerals stop at 3,999, written MMMCMXCIX. This converter reads only the form it writes, so a spelling such as MV̅ for 4,000 gets a message.

What is the largest number this converter handles?

3,999,999, written M̅M̅M̅C̅M̅X̅C̅I̅X̅CMXCIX. A larger one would need four barred Ms in a row, which breaks the three-in-a-row rule.

Where are Roman numerals still used?

Clock faces, book chapters, monument dates, Super Bowl numbers, movie sequels (Star Wars Episode VIII), and pope/king regnal names (Pope John XXIII).