Should 4 be written as IV or IIII in Roman numerals?

The standard subtractive form is IV, and that is what this converter outputs. IIII appears on some clock faces for visual symmetry but is not standard, so the decoder treats it as invalid.

What is the largest number Roman numerals can represent?

With the standard symbols the maximum is 3999, written MMMCMXCIX. Enable overline (vinculum) notation and the converter reaches 3,999,999, since a bar over a numeral multiplies its value by 1,000.

Why is there no Roman numeral for zero?

The Roman system is additive and had no digit for zero; the Latin word nulla was used in text instead. This converter therefore starts at 1 and rejects 0 and negative numbers.

What does the bar (overline) over a Roman numeral mean?

An overline, called a vinculum, multiplies the numeral beneath it by 1,000. So V with a bar is 5,000 and X with a bar is 10,000. Toggle it on to convert numbers above 3999.

Can this tool decode lowercase Roman numerals?

Yes. Input such as 'mcmxciv' or numerals with stray spaces is normalized to uppercase and trimmed before decoding, so you do not have to clean it up first.

How does the converter know a Roman numeral is invalid?

It parses your input to a number, re-encodes that number in canonical form, and compares the two. If they differ — as with IIII, VV, or IC — the input is flagged as malformed.

Roman Numeral Converter

Convert numbers to Roman numerals and decode them back in your browser, with standard 1–3999 support and optional overline notation for larger values.

The Roman Numeral Converter runs entirely in your browser. The numbers and numerals you type or paste are converted on your device and are never uploaded to ArrayKit.

Open the Number Base Converter

About Roman Numeral Converter

The Roman Numeral Converter turns any whole number into its Roman numeral form and decodes Roman numerals back into ordinary numbers. Flip between the two directions with one toggle: type 1994 to get MCMXCIV, or paste MCMXCIV to read 1994. It covers the standard 1 to 3999 range using subtractive notation, and can render larger values with overline (vinculum) notation, where a bar over a numeral multiplies it by 1,000. The decoder validates input as you type, rejecting malformed sequences like IIII or VV and explaining what is wrong. It is handy for dating copyrights, numbering chapters and outlines, reading clock faces and monuments, or teaching how the system works. Everything runs locally in your browser, so the numbers you convert never leave your device.

Features

Convert whole numbers to Roman numerals and decode numerals back to numbers
One toggle switches between number-to-Roman and Roman-to-number
Covers the standard 1–3999 range using subtractive notation (IV, IX, XL, CM)
Optional overline (vinculum) notation extends the range up to 3,999,999
Validates Roman input and rejects malformed forms like IIII, VV, or IC
Accepts lowercase and spaced numerals, normalizing them before decoding
One-click copy for the resulting numeral or the decoded number
Runs entirely in your browser — nothing you convert is uploaded

How to use the Roman Numeral Converter

Keep Number → Roman selected and type a whole number such as 2024
Copy the Roman numeral, or turn on overline to encode values above 3999
Switch to Roman → Number and paste a numeral like MMXXIV
Read the decoded number, or fix the issue the validator points out

Example

Input

Output

MCMXCIV

1000 (M) + 900 (CM) + 90 (XC) + 4 (IV) = 1994.

Common errors & troubleshooting

Entering 4000 or higher shows an out-of-range message. — Standard Roman numerals stop at 3999. Turn on overline (vinculum) notation to go higher — a bar over a numeral multiplies its value by 1,000, reaching 3,999,999.
'IIII' or 'VV' is rejected as invalid. — A symbol repeats at most three times and V, L, D never repeat. Use the subtractive form — IV for 4 — which the converter produces for you automatically.
Decoding 'IC' does not return 99. — Only the pairs IV, IX, XL, XC, CD, and CM are valid subtractions. 'IC' is not a legal form for 99; the correct numeral is XCIX.
A zero or negative number will not convert. — Roman numerals have no symbol for zero and cannot express negatives. Enter a whole number of 1 or greater to convert.

Frequently asked questions

Should 4 be written as IV or IIII in Roman numerals?: The standard subtractive form is IV, and that is what this converter outputs. IIII appears on some clock faces for visual symmetry but is not standard, so the decoder treats it as invalid.
What is the largest number Roman numerals can represent?: With the standard symbols the maximum is 3999, written MMMCMXCIX. Enable overline (vinculum) notation and the converter reaches 3,999,999, since a bar over a numeral multiplies its value by 1,000.
Why is there no Roman numeral for zero?: The Roman system is additive and had no digit for zero; the Latin word nulla was used in text instead. This converter therefore starts at 1 and rejects 0 and negative numbers.
What does the bar (overline) over a Roman numeral mean?: An overline, called a vinculum, multiplies the numeral beneath it by 1,000. So V with a bar is 5,000 and X with a bar is 10,000. Toggle it on to convert numbers above 3999.
Can this tool decode lowercase Roman numerals?: Yes. Input such as 'mcmxciv' or numerals with stray spaces is normalized to uppercase and trimmed before decoding, so you do not have to clean it up first.
How does the converter know a Roman numeral is invalid?: It parses your input to a number, re-encodes that number in canonical form, and compares the two. If they differ — as with IIII, VV, or IC — the input is flagged as malformed.

Related tools

Number to Words Converter — Convert numbers and currency amounts into written words, with cardinal and ordinal forms.
Number Base Converter — Convert integers between binary, octal, decimal and hex.
Bitwise Calculator — Apply AND, OR, XOR, NOT and bit shifts to integers, with binary, hex and decimal views.
IEEE 754 Converter — Convert decimals to and from 32-bit and 64-bit IEEE 754 floating-point, with the bit fields.
Base32 Encoder / Decoder — Encode text to Base32 and decode Base32 back to text (RFC 4648), in your browser.
Text to Binary Converter — Convert text to binary, and binary, hex or decimal back to text, in your browser.