Free tool

Roman numeral converter

Convert Arabic numbers to Roman numerals and Roman numerals to Arabic numbers instantly. Supports 1 to 3999 with real-time validation.

100% free
No sign-up
No limits
Instant results

Conversion mode

Arabic number (1-3999)

Roman numeral

roman

Roman numeral will appear here

Reference table

100

500

1,000

Common examples

What this tool does

Two-way conversion: Arabic to Roman and Roman to Arabic
Real-time conversion as you type
Validation with clear error messages
Reference table and common examples
One-click copy output
100% browser — no server calls

Want the full picture?

This tool fixes one thing. Our scanner runs 240+ checks across 10 SEO pillars and hands you a prioritised fix list — plus a savage AI roast.

Run a free audit

What is Roman Numeral Converter?

A Roman numeral converter is an online tool that translates between the modern Arabic number system (1, 2, 3...) and the ancient Roman numeral system (I, II, III...). Roman numerals use seven symbols — I (1), V (5), X (10), L (50), C (100), D (500), and M (1000) — combined according to specific rules to represent any number from 1 to 3999. The standard Roman numeral system uses subtractive notation where placing a smaller value before a larger one means subtraction (IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900). This converter works in both directions: enter an Arabic number to get the Roman numeral equivalent, or enter a Roman numeral to get the Arabic number. The tool validates input in real time, catching invalid combinations and out-of-range values instantly. All conversion runs entirely in your browser with zero server interaction, making it fast and private.

How to use Roman Numeral Converter

1
Select your conversion mode
Choose between "Number to Roman" to convert Arabic numbers (like 2026) into Roman numerals, or "Roman to Number" to convert Roman numerals (like MMXXVI) back into Arabic numbers. Click the toggle buttons at the top to switch modes.
2
Enter your value
Type your number or Roman numeral into the input field. The converter works in real time — your result appears instantly as you type. For Arabic numbers, enter any whole number from 1 to 3999. For Roman numerals, use the letters M, D, C, L, X, V, and I.
3
Copy or explore examples
Click the Copy button next to the output to copy the result to your clipboard. Use the common examples section to quickly load popular conversions like years, clock numbers, or the maximum value 3999. The reference table shows all seven Roman numeral symbols and their values.

Features

Two-way conversion between Arabic numbers and Roman numerals with a single toggle
Real-time conversion that updates instantly as you type each character
Input validation with clear error messages for invalid numbers or numeral combinations
Reference table showing all seven Roman numeral symbols (I, V, X, L, C, D, M) and their values
Eight common examples including years, clock numbers, and edge cases you can load with one click
Round-trip validation ensures Roman numeral output matches standard canonical form
One-click copy button to copy the converted result to your clipboard instantly
Zero server calls — all conversion logic runs entirely in your browser for instant results

Related tools

Unix Timestamp Converter

Convert Unix timestamps to human-readable dates and back. Supports seconds and milliseconds.

Open tool

Number Base Converter

Convert numbers between binary, octal, decimal and hexadecimal bases instantly.

Open tool

Temperature Converter

Convert between Celsius, Fahrenheit and Kelvin with instant results and formula display.

Open tool

Unit Converter

Convert length, weight, volume, speed, area and data units. 50+ unit types supported.

Open tool

Byte Converter

Convert between bytes, KB, MB, GB, TB and PB. Binary (1024) and decimal (1000) modes.

Open tool

Binary to Text Converter

Convert binary code to ASCII text and text to binary. Supports 8-bit encoding.

Open tool

See all Conversion tools

Frequently asked questions

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

The standard Roman numeral system supports numbers from 1 to 3999. The largest value is 3999, written as MMMCMXCIX. Numbers above 3999 require extended notation with vinculum (overline bars) to multiply values by 1000, which is not part of the standard system supported by this converter.

Why is 4 written as IV instead of IIII?

Standard Roman numerals use subtractive notation where placing a smaller value before a larger one means subtraction. IV means 5 minus 1, which equals 4. This reduces repetition and keeps numerals shorter. However, some clock faces use IIII instead of IV — this is a traditional exception, not the standard rule. This converter uses the standard subtractive form.

How do I convert a year to Roman numerals?

Enter the year as an Arabic number in "Number to Roman" mode. For example, 2026 converts to MMXXVI (M+M = 2000, X+X = 20, V+I = 6). The tool handles all years from 1 to 3999 automatically. You can also click the "2026 (current year)" example to load it instantly.

What Roman numerals are valid?

Valid Roman numerals use only the letters M, D, C, L, X, V, and I, combined according to strict rules. A symbol can be repeated up to three times consecutively (III = 3, XXX = 30). Only I, X, and C can be used in subtractive pairs (IV, IX, XL, XC, CD, CM). This converter validates your input against these rules and shows an error for invalid combinations.

Is the conversion done on a server?

No. All conversion logic runs entirely in your browser using JavaScript. Nothing is sent to any server. This means the tool works offline, has zero latency, and your input remains completely private. The page loads once and all subsequent conversions happen locally.

Can I convert zero or negative numbers?

No. The Roman numeral system has no symbol for zero and does not support negative numbers. The system was developed by the ancient Romans for counting and recording positive quantities. This converter accepts whole numbers from 1 to 3999 only and will show a validation error for anything outside that range.

What is Roman Numeral Converter?

How to use Roman Numeral Converter

Select your conversion mode

Choose between "Number to Roman" to convert Arabic numbers (like 2026) into Roman numerals, or "Roman to Number" to convert Roman numerals (like MMXXVI) back into Arabic numbers. Click the toggle buttons at the top to switch modes.

Enter your value

Type your number or Roman numeral into the input field. The converter works in real time — your result appears instantly as you type. For Arabic numbers, enter any whole number from 1 to 3999. For Roman numerals, use the letters M, D, C, L, X, V, and I.

Copy or explore examples

Click the Copy button next to the output to copy the result to your clipboard. Use the common examples section to quickly load popular conversions like years, clock numbers, or the maximum value 3999. The reference table shows all seven Roman numeral symbols and their values.

Features

Two-way conversion between Arabic numbers and Roman numerals with a single toggle

Real-time conversion that updates instantly as you type each character

Input validation with clear error messages for invalid numbers or numeral combinations

Reference table showing all seven Roman numeral symbols (I, V, X, L, C, D, M) and their values

Eight common examples including years, clock numbers, and edge cases you can load with one click

Round-trip validation ensures Roman numeral output matches standard canonical form

One-click copy button to copy the converted result to your clipboard instantly

Zero server calls — all conversion logic runs entirely in your browser for instant results

Frequently asked questions

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

Why is 4 written as IV instead of IIII?

How do I convert a year to Roman numerals?

What Roman numerals are valid?

Is the conversion done on a server?

Can I convert zero or negative numbers?