How to write 420 in Roman numerals
Roman numerals are built place by place, from the largest value to the smallest. For 420 the places are 400 (hundreds), 20 (tens).
- Write 400 as
CD. - Write 20 as
XX.
Joined together, CD + XX gives CDXX.
420 digit by digit
| Place | Value | Numeral | Rule used |
|---|---|---|---|
| hundreds | 400 | CD | subtractive: one symbol before the five symbol |
| tens | 20 | XX | the symbol repeated twice |
Check CDXX by reading it back
Reading CDXX from left to right and adding the pieces: CD = 400, XX = 20. Together that is 400 + 20 = 420, so CDXX and 420 match.
Mistakes to avoid with CDXX
- Do not write the 4s and 9s additively. 420 uses subtractive pairs (
CDfor 400), not strings like IIII or VIIII. - Never repeat a symbol more than three times in a row. When a fourth would be needed, the subtractive form takes over.
- Only I, X and C may be placed before a larger symbol to subtract, so CDXX never contains forms such as VX or LC.
- Read CDXX as one number, not letter by letter: add the values left to right, except where a smaller symbol sits before a larger one.
Facts about the number 420
- 420 is an even number and composite, with prime factors 22 x 3 x 5 x 7.
- In binary 420 is
110100100and in hexadecimal it is1A4. - Written out, 420 is "four hundred twenty".
- The digits of 420 add up to 6, so it is divisible by 3.
Where you will see 420 in Roman numerals
Readers might find 420 written as CDXX in the introductory pages of exhaustive legal or governmental publications. Agencies use Roman numerals for front matter to maintain a strict visual separation between prefaces and the primary document content.
Numbers near 420
| Number | Roman numeral |
|---|---|
| 418 | CDXVIII |
| 419 | CDXIX |
| 420 | CDXX |
| 421 | CDXXI |
| 422 | CDXXII |
FAQ
What is 420 in Roman numerals?
420 is written CDXX in Roman numerals. It is built from CD (400), XX (20).
How do you write 420 in lowercase Roman numerals?
Lowercase Roman numerals use the same rules, so 420 is cdxx. Lowercase is common for page numbers in a book's preface and for outline levels.
How do I convert any number to Roman numerals?
Split the number into thousands, hundreds, tens and ones, write each part with the symbols I, V, X, L, C, D and M, then join them from largest to smallest. Or paste it into the Roman numeral converter, which also converts back.
More roman numerals
- 400 (CD): previous page
- 450 (CDL): next page
- Roman numerals chart: the full list