420 in Roman Numerals
Four hundred twenty is written CDXX in Roman numerals. It uses the subtractive rule, where a smaller glyph placed before a larger one is taken away rather than added, which keeps the numeral short and is the part most people find fiddly.
How CDXX is formed
Reading left to right, 420 breaks into these additive parts. Each Roman symbol is added in turn to reach the total.
CD + X + X = 400 + 10 + 10 = 420.
Where 420 in Roman numerals is used
- Monarch and pope names, for example the 420th of a royal line.
Convert another number
420 is written CDXX in Roman numerals.
Frequently asked questions
How do you write 420 in Roman numerals?
Write 420 as CDXX, combining CD + X + X. Start from the largest value that fits and work down until nothing is left over.
Why is 420 not written CCCCXX?
CDXX uses the subtractive rule: a smaller symbol placed before a larger one is taken away, so you never repeat a symbol four times. CCCCXX breaks that rule, which is why CDXX is the only correct form.
How is CDXX broken down?
CDXX breaks down as CD (400), X (10), X (10), so CD + X + X = 400 + 10 + 10 = 420.
What number is CDXX?
CDXX is 420. Read the symbols left to right, treat any smaller-before-larger pair as a single subtraction, and add the groups together.