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31 in Roman Numerals

31 in Roman numerals is XXXI. It breaks down as XXX + I, which adds up to 30 + 1 = 31.

  • Roman numeral
    XXXI
  • Lowercase
    xxxi
  • Breakdown
    XXX + I
  • In words
    thirty-one
  • Binary
    11111
  • Hexadecimal
    1F

How to write 31 in Roman numerals

Roman numerals are built place by place, from the largest value to the smallest. For 31 the places are 30 (tens), 1 (ones).

  1. Write 30 as XXX.
  2. Write 1 as I.

Joined together, XXX + I gives XXXI.

31 digit by digit

PlaceValueNumeralRule used
tens30XXXthe symbol repeated three times (the limit)
ones1Ione symbol

Check XXXI by reading it back

Reading XXXI from left to right and adding the pieces: XXX = 30, I = 1. Together that is 30 + 1 = 31, so XXXI and 31 match.

Mistakes to avoid with XXXI

  • 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 XXXI never contains forms such as VX or LC.
  • Read XXXI 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 31

  • 31 is an odd number and a prime number.
  • In binary 31 is 11111 and in hexadecimal it is 1F.
  • Written out, 31 is "thirty-one".
  • The digits of 31 add up to 4.

Where you will see 31 in Roman numerals

People see 31 written as XXXI on the title pages of books that use Roman numerals for preliminary pages. Publishers choose this format to clearly separate front matter from the main text, which uses standard Arabic numbers.

Numbers near 31

NumberRoman numeral
29XXIX
30XXX
31XXXI
32XXXII
33XXXIII

FAQ

What is 31 in Roman numerals?

31 is written XXXI in Roman numerals. It is built from XXX (30), I (1).

How do you write 31 in lowercase Roman numerals?

Lowercase Roman numerals use the same rules, so 31 is xxxi. 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