What Number Is XVIII? Read Any Roman Numeral Fast

XVIII is 18: X is 10, V is 5 and each I is 1, so 10 + 5 + 1 + 1 + 1 = 18. Every symbol is the same size or smaller than the one before it, so you just add. That's the whole trick for most numerals, and a three-step method covers the rest.

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  1. Step 1: look for a small symbol before a bigger one
  2. Step 2: add everything
  3. Step 3: check that it makes sense
  4. The same method, symbol by symbol
  5. Practice
  6. Numerals that look alike

Step 1: look for a small symbol before a bigger one

Scan the numeral from left to right. If you find a symbol followed by a bigger one, those two form a pair, and the pair is worth the bigger minus the smaller. There are only six such pairs:

The seven symbols and the six subtractive pairs
  • I1
  • V5
  • X10
  • L50
  • C100
  • D500
  • M1,000
  • IV4
  • IX9
  • XL40
  • XC90
  • CD400
  • CM900

XVIII has none: X, V, I, I, I all go down or stay the same. XIX has one: the IX at the end.

Step 2: add everything

Each pair counts as one value, every other symbol counts on its own. Then add:

  • XVIII → X + V + I + I + I = 10 + 5 + 1 + 1 + 1 = 18
  • XIX → X + IX = 10 + 9 = 19
  • XLIV → XL + IV = 40 + 4 = 44
  • MCMLXXXIV → M + CM + L + X + X + X + IV = 1000 + 900 + 50 + 30 + 4 = 1984

Step 3: check that it makes sense

Two quick checks catch nearly every misreading:

  1. The groups go down. After you've grouped the pairs, the values should never go up from left to right.
  2. No symbol appears four times in a row. XVIIII is not 19; the standard form is XIX.

If a numeral fails a check, it isn't standard. The validator checks it for you.

The same method, symbol by symbol

Here is 18 read one symbol at a time, with the running total:

SymbolsValueRunning total
X1010
V515
I116
I117
I118
XVIII18

Practice

Try these before you look at the answers in the table.

NumeralGroupsValue
XIVX · IV14
XXVIIX · X · V · I · I27
XLIXXL · IX49
LXXXVIIIL · X · X · X · V · I · I · I88
XCIXXC · IX99
CDXLIVCD · XL · IV444

When the steps feel automatic, take the quiz to practise on numerals you haven't seen.

Numerals that look alike

A few pairs trip people up because they use the same letters:

  • XVIII and XIIX. The first is 18. The second isn't valid, because only one symbol can subtract.
  • XIX and XXI. 19 and 21: the position of the I changes everything.
  • IV and VI. 4 and 6, for the same reason.
Convert a numeralType any Roman numeral to read it, or any number from 1 to 3999 to write it.