Roman Numerals: A Complete Guide

The Seven Roman Numeral Symbols

The entire Roman numeral system is built from just seven symbols:

Symbol	Value	Mnemonic
I	1	One finger
V	5	V-shape of hand (5 fingers)
X	10	Two V's crossed
L	50	Half of C (100)
C	100	Latin "centum" (hundred)
D	500	Half of M (1000)
M	1000	Latin "mille" (thousand)

The Rules: Additive and Subtractive Notation

Additive rule: When a symbol appears after a larger or equal symbol, add its value. III = 1+1+1 = 3. VIII = 5+1+1+1 = 8. XVI = 10+5+1 = 16.

Subtractive rule: When a smaller symbol appears before a larger symbol, subtract it. IV = 5−1 = 4. IX = 10−1 = 9. XL = 50−10 = 40. XC = 100−10 = 90. CD = 500−100 = 400. CM = 1000−100 = 900.

The six valid subtractive combinations are:

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

No other subtractive combinations are valid in standard notation. You cannot write IC for 99 — the correct form is XCIX (90+9).

How to Read a Roman Numeral Step by Step

To convert MCMXCIV to decimal:

1. M = 1000
2. CM = 900 (C before M → subtract 100 from 1000)
3. XC = 90 (X before C → subtract 10 from 100)
4. IV = 4 (I before V → subtract 1 from 5)
5. Total: 1000 + 900 + 90 + 4 = 1994

How to Write a Roman Numeral Step by Step

To convert 2026 to Roman numerals:

1. 2026 ÷ 1000 = 2 → MM (2000 used, 26 remaining)
2. 26 ÷ 10 = 2 → XX (20 used, 6 remaining)
3. 6 = V + I → VI (5+1)
4. Result: MMXXVI

Roman Numerals Reference: 1–20 and Key Values

I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII, XIV, XV, XVI, XVII, XVIII, XIX, XX

Key values: XXX=30, XL=40, L=50, LX=60, LXX=70, LXXX=80, XC=90, C=100, CC=200, CCC=300, CD=400, D=500, DC=600, DCC=700, DCCC=800, CM=900, M=1000, MM=2000, MMM=3000, MMMCMXCIX=3999.

Use our Roman Numeral Converter to convert any number instantly — both decimal to Roman and Roman to decimal.

Frequently Asked Questions

What are the seven Roman numeral symbols?

The seven symbols are: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. All Roman numerals are built from combinations of these seven values using additive and subtractive notation.

Why is 4 written as IV and not IIII in Roman numerals?

The IV notation uses subtractive notation — a smaller value before a larger value means subtract. IV = 5 − 1 = 4. This convention was not strictly universal in ancient Rome (IIII was also used and still appears on many clock faces). Modern standard style uses IV for 4.

What is the largest number that can be written in Roman numerals?

In standard notation, 3,999 (MMMCMXCIX) is the largest. To represent larger numbers, a bar over a symbol multiplies it by 1,000. In practice, standard Roman numerals are used for numbers up to a few thousand.

Where are Roman numerals still used today?

Roman numerals are still used in: movie copyright notices (MMXXVI for 2026), chapter and section numbering in books, clock and watch faces, Olympic Games year designations, Super Bowl numbering, monarch regnal numbers (King Charles III), and building construction dates on facades.