What does CDXXIII mean?

CDXXIII is the Roman numeral for 423 — 400 + 10 + 10 + 1 + 1 + 1.

How do you write 423 in Roman numerals?

Take the largest value that fits and repeat until nothing is left: CD (400), then X (10), then X (10), then I (1), then I (1), then I (1). That gives CDXXIII.

423 in Roman numerals

CDXXIII

Number (1–3,999 for numerals)

Roman numeral

423 is written CDXXIII in Roman numerals. That is 6 symbol groups added together, reading left to right from the largest value down.

How it breaks down

CDXXIII = 400 + 10 + 10 + 1 + 1 + 1 = 423
Group	Value	Subtraction	Running total
CD	400	D − C	400
X	10	—	410
X	10	—	420
I	1	—	421
I	1	—	422
I	1	—	423

Why the smaller symbol comes first

CDXXIII uses subtractive notation in one place: CD means D minus C, or 400. A smaller symbol placed before a larger one is subtracted from it rather than added, which is why IX is nine and not eleven.

Only six such pairs are valid — IV, IX, XL, XC, CD and CM. That restriction is what makes the notation unambiguous: IIII and IC both look like they should work, but neither is standard, and only one spelling of any number is correct.

The symbols

Symbol	Value	Used here
I	1	yes — 3×
V	5	no
X	10	yes — 2×
L	50	no
C	100	yes — 1×
D	500	yes — 1×
M	1,000	no

The same number, other ways

In words: Four hundred twenty-three
Roman numeral: CDXXIII
Symbol count: 7 characters
Binary: 110100111
Hexadecimal: 1A7

The numbers either side

Number	Roman numeral
421	CDXXI
422	CDXXII
423	CDXXIII ←
424	CDXXIV
425	CDXXV

Common questions

What is 423 in Roman numerals?: 423 is CDXXIII.
What does CDXXIII mean?: CDXXIII is the Roman numeral for 423 — 400 + 10 + 10 + 1 + 1 + 1.
How do you write 423 in Roman numerals?: Take the largest value that fits and repeat until nothing is left: CD (400), then X (10), then X (10), then I (1), then I (1), then I (1). That gives CDXXIII.

Sources

Calculated on this page — At One Place

How these figures are compiled and checked