How many characters are there when 2019 is written in Roman numerals?

The number 2019 is written in Roman numerals is MMXIX. Where MM is 2,000, X is 10 and IX is 9.

The Roman numbers from 1 to 10 are generally written as

I, II, III, IV, V, VI, VII, VIII, IX, X.

The multiples of 10, from 10 to 100, are written according to the same pattern, with X, L, and C taking the place of I, V, and X

X, XX, XXX, XL, L, LX, LXX, LXXX, XC, C.

Note that 40 is usually written XL ("10 less than 50") rather than XXXX, and 90 as XC ("10 less than 100") rather than LXXXX.

Similarly, the multiples of 100, 100 to 1000, are written as

C, CC, CCC, CD, D, DC, DCC, DCCC, CM, M.

where CD is to be read as "100 less than 500" (that is, 400), and CM as "100 less than 1000" (that is, 900).

Since the system has no standard symbols for 5,000 and 10,000, the full pattern cannot be extended to the multiples of 1000 – restricting the "thousands" range of "normal" Roman numerals to 1,000, 2,000 and 3,000:

M, MM, MMM.