Learn Roman Numerals for School
Practice converting between Roman numerals and decimal numbers for history, math, and classical studies.
Common values
Roman numeral rules: I=1, V=5, X=10, L=50, C=100, D=500, M=1000.
Subtractive notation: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Standard numerals max out at MMMCMXCIX (3999).
Vinculum: a bar over a numeral multiplies it by 1000 (V̅ = 5000, X̅ = 10000, M̅ = 1,000,000), extending the range to 3,999,999.
Education tips
Use the preset buttons to explore tricky conversions: 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD), 900 (CM) — these are the subtractive notation cases.
Subtractive notation rule: when a smaller symbol precedes a larger one, subtract it. IV = 5−1 = 4. XL = 50−10 = 40. CM = 1000−100 = 900.
Romans didn't have zero or negative numbers. The system only goes from 1 to 3999. Numbers beyond 3999 required special notation not in standard use.
Test yourself: convert 1999 before checking. It's MCMXCIX (M=1000, CM=900, XC=90, IX=9). Complicated but follows the rules!
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