Number
400 in Roman numerals
400 is written CD
Type any other number or numeral below to convert it.
Above 3,999? Type the barred part in brackets, e.g. (IV)CC = 4,200.
How CD is built
Roman numerals are written one decimal place at a time, largest first.
- CDhundreds · 4C before D means 500 − 100 = 400. This saves writing CCCC.
The pair CD uses subtraction: a smaller letter before a larger one is taken away from it. Only six pairs work this way: IV, IX, XL, XC, CD and CM. More on subtraction
Mistakes to avoid
- Not CCCC (4 letters). That adds everything up without subtraction. The Romans sometimes wrote numbers this way, and clocks still show 4 as IIII, but today CD (2 letters) is the standard.
- There's no letter for zero. The zeros are simply left out, which is why 400 has 1 part, not 3.
About the number 400
- 400 is even and can be split into prime factors: 2 × 2 × 2 × 2 × 5 × 5, or in Roman numerals II × II × II × II × V × V.
- 400 is a square number: 20 × 20 (XX × XX).
- CD has 2 letters. 969 of the numbers up to 1,000 have longer numerals.
Counting from 391 to 400
| Number | Roman numeral |
|---|---|
| 391 | CCCXCI |
| 392 | CCCXCII |
| 393 | CCCXCIII |
| 394 | CCCXCIV |
| 395 | CCCXCV |
| 396 | CCCXCVI |
| 397 | CCCXCVII |
| 398 | CCCXCVIII |
| 399 | CCCXCIX |
| 400 | CD |