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Roman Numeral Calculator

Convert to and from Roman numerals and do arithmetic in them.

Calculators Reviews Free · no sign-up

Convert

Type into either box.

Breakdown

Arithmetic in numerals

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The symbols

I1
V5
X10
L50
C100
D500
M1000

Quick Tool Overview

The Roman Numeral Calculator converts a number into Roman numerals and reads a numeral back into a number, with the value of each symbol broken out. Subtractive notation is validated properly, which is where most converters get sloppy.

What it does
Converts Roman numerals both ways and does arithmetic in them
You give it
A number from 1 to 3,999, or a Roman numeral
You get back
The conversion with a symbol-by-symbol breakdown
Best for
Dates, chapter numbers, clock faces, tattoos and homework
Calculators Free, unlimited use No sign-up Runs in your browser

About the Roman Numeral Calculator

Convert a number into Roman numerals or read a numeral back into a number, with the value of each symbol broken out so you can see how the total is assembled. Arithmetic works directly on numerals too.

Subtractive notation is validated properly, which is where most converters get sloppy. Four is IV, not IIII, and 1999 is MCMXCIX rather than the tempting but invalid MIM. Only I, X and C can be subtracted, and only from the next two higher symbols, so IL and IC are not valid numerals however sensible they look. The system also has no zero and no negative numbers, and runs to 3,999 in standard form.

Key features of the Roman Numeral Calculator

Strict subtractive notation

Four is IV, not IIII, and 1999 is MCMXCIX rather than the tempting but invalid MIM.

Real validation

Only I, X and C can be subtracted, and only from the next two higher symbols, so IL and IC are rejected however sensible they look.

Symbol breakdown

Each symbol's value is listed so you can see how the total is assembled.

Arithmetic in numerals

Add and subtract numerals directly, with the result returned as a valid numeral.

Limits explained

The system has no zero and no negatives and runs to 3,999 in standard form — the tool says so rather than failing quietly.

How to use the Roman Numeral Calculator

  1. 1

    Type a number or a numeral

    Enter either form and the other is produced instantly.

  2. 2

    Check the breakdown

    Each symbol is listed with its value, including any subtractive pairs.

  3. 3

    Do arithmetic

    Add or subtract two numerals and the answer is returned as a valid Roman numeral.

Frequently asked questions

I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1,000. Everything else is built by combining them.

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