roman numerals calculator - Aaron Graves, PhDude Replica

Convert Number to Roman Numeral

Enter a whole number (1 to 3999)

Result will appear here.

Convert Roman Numeral to Number

Enter a valid Roman numeral

Result will appear here.

Roman Numeral Arithmetic

First value (Roman numeral or whole number)

Operator

Second value (Roman numeral or whole number)

Roman numerals do not represent zero, negative numbers, or non-integers. The tool will note when a Roman result is not representable.

Calculation result will appear here.

What this Roman numerals calculator does

This page gives you a simple Roman numeral converter and calculator in one place. You can convert regular numbers (also called Arabic numerals) into Roman numerals, convert Roman numerals back into numbers, and run arithmetic using either format.

Whether you are checking a date on a clock face, decoding chapter numbers in a book, or helping a student learn numeral systems, this tool saves time and reduces mistakes.

How to use the calculator

1) Number to Roman numeral

Enter any whole number from 1 to 3999 and click Convert to Roman. The calculator uses standard modern notation: IV for 4, IX for 9, XL for 40, XC for 90, CD for 400, and CM for 900.

2) Roman numeral to number

Type a Roman numeral such as MMXXVI and click Convert to Number. The input is validated to make sure it follows accepted Roman numeral patterns.

3) Roman numeral arithmetic

Enter two values and choose +, -, ×, or ÷. You can mix styles (for example, XII + 8). The result is always shown as a number, and as a Roman numeral when possible.

Roman numeral reference chart

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

Key subtraction rules

I can appear before V or X (IV = 4, IX = 9)
X can appear before L or C (XL = 40, XC = 90)
C can appear before D or M (CD = 400, CM = 900)

Common mistakes this tool helps you avoid

Writing invalid repeats like VV or LL
Using incorrect subtraction patterns like IL for 49 (correct is XLIX)
Forgetting that Roman numerals traditionally do not represent zero
Trying to represent decimals as Roman numerals in standard modern form

Why Roman numerals still matter

Roman numerals still appear in book chapters, movie sequels, monarch names, clocks, sporting events, and formal outlines. Learning the system improves number pattern recognition and historical literacy, and it can also be a fun logic exercise.

Quick examples

2026 → MMXXVI
XLIV → 44
XIV + IX = XXIII (23)
C ÷ IV = 25, Roman result: XXV

If you are practicing Roman numeral conversion, bookmark this calculator and use it as a quick checker while you learn.