Roman Numeral Converter – Numbers to Roman Numerals & Back

Convert numbers 1–3999 to Roman numerals, or paste a Roman numeral like MMXXV and get the number back. Includes a step-by-step breakdown, validation, and a full reference chart. Free, private, and runs entirely in your browser.

Convert

Number → Roman numeral

Enter a number (1–3999) Type to convert instantly

Quick examples

Tip: Roman numerals are case-insensitive here — mmxxv and MMXXV both work. Standard form uses uppercase.

Result

Waiting for input

Roman numeral

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Quick reference (1–100)

Number	Roman	Number	Roman

What is a Roman numeral converter?

A Roman numeral converter translates between standard Arabic numbers (1, 2, 3…) and Roman numerals (I, II, III…). This tool works both ways: enter a number to get the Roman numeral, or paste a Roman numeral to get the number back. Everything runs in your browser — nothing is sent to a server.

Roman numerals use seven symbols, each with a fixed value:

Symbol	Value	Symbol	Value
I	1	V	5
X	10	L	50
C	100	D	500
M	1000

Numbers are formed by combining these symbols. Most of the time, symbols are written from largest to smallest and their values are added: XVI = 10 + 5 + 1 = 16. When a smaller symbol appears before a larger one, its value is subtracted instead: IV = 5 − 1 = 4.

How Roman numeral conversion works

The converter uses a greedy algorithm for number-to-Roman conversion and a left-to-right comparison for Roman-to-number conversion.

Number → Roman numeral

The algorithm iterates through a lookup table of values from largest to smallest. For each value, it appends the corresponding symbol as many times as it fits, then subtracts that value from the remaining number. The lookup table includes all subtractive forms:

M = 1000, CM = 900, D = 500, CD = 400
C = 100, XC = 90, L = 50, XL = 40
X = 10, IX = 9, V = 5, IV = 4
I = 1

For example, converting 2025: M fits twice (2000 left), X fits twice (5 left), V fits once (0 left) → MMXXV. The step-by-step breakdown in the tool shows this process live.

Roman numeral → Number

The algorithm scans the Roman numeral from left to right. If a symbol's value is less than the next symbol's value, it's subtracted; otherwise it's added. So XIV becomes: 10 (X) + (5−1) (IV) = 14. This correctly handles all subtractive forms including IV, IX, XL, XC, CD, and CM.

The valid range: 1 to 3999

Standard Roman numerals are limited to 1–3999. The largest standard numeral is MMMCMXCIX (3999) because no symbol can be repeated more than three times in a row. Numbers above 3999 require non-standard notation — typically an overline (vinculum) to multiply a symbol by 1000, like IV̅ for 4000 — which is not part of the classic system and is not supported by this converter.

Inputs outside 1–3999 will trigger a validation error with a clear explanation.

Subtractive notation: the six special cases

Roman numerals use subtractive notation to avoid writing four identical symbols in a row. There are exactly six valid subtractive pairs:

Pair	Value	Why
IV	4	Instead of IIII (5 − 1)
IX	9	Instead of VIIII (10 − 1)
XL	40	Instead of XXXX (50 − 10)
XC	90	Instead of LXXXX (100 − 10)
CD	400	Instead of CCCC (500 − 100)
CM	900	Instead of DCCCC (1000 − 100)

Only I, X, and C can be used as subtractive prefixes, and only before V, L, and D respectively (plus X before C, and C before M). The converter enforces these rules and will reject malformed numerals like IIV or VX.

Frequently asked questions

What is a Roman numeral converter?

A Roman numeral converter is a tool that translates between standard Arabic numbers (1, 2, 3…) and Roman numerals (I, II, III…). It handles both directions: you can enter a number and get the Roman numeral, or enter a Roman numeral and get the number back.

What is the range of this converter?

This converter supports numbers from 1 to 3999. The largest standard Roman numeral is MMMCMXCIX (3999). Numbers above 3999 require overlines or other non-standard notation, which is not supported here.

How do Roman numerals work?

Roman numerals use seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Numbers are formed by combining these symbols, usually from largest to smallest (addition). When a smaller symbol appears before a larger one, it is subtracted — for example, IV is 4 and IX is 9.

Is this Roman numeral converter free?

Yes, completely free. No signup, no watermark, no hidden charges. Convert as many numbers as you want for personal or commercial use.

Does it work for Roman numerals like IV, IX, and XL?

Yes. The converter handles all standard subtractive forms: IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). It also validates input and will flag invalid Roman numerals.

Is my data safe?

Absolutely. Everything runs in your browser. The values you enter never leave your device — there is no server processing, no logging, and no data storage.

Can I use this on my phone?

Yes. The converter is fully responsive and works on phones, tablets, and desktops.

What does the step-by-step breakdown show?

When you convert a number to a Roman numeral, the breakdown lists every symbol that was used and its value, so you can see exactly how the numeral was built. This is useful for learning Roman numerals or checking your work.