Put a smaller sign after a larger one: add
V is 5 and I is 1. In VI, the I comes after the V: 5 + 1 = 6.
ANCIENT · ADDITIVE · SUBTRACTIVE
Roman
Letters represent values that are added or subtracted: XLII = 50 − 10 + 2.
Convert numbers- Place
- Ancient Rome; international use
- Period / variant
- Antiquity–present
EXAMPLES
42 · Additive · subtractive
XLII: fifty minus ten, plus two.
Worked example
Write 42 in Roman
Read from left to right. Treat an allowed subtraction pair as one group, then add the groups.
Read XL together: X = 10 comes before the larger L = 50. This allowed subtraction pair means 50 − 10 = 40.
I means 1. II repeats it 2 times: 1 + 1 = 2.
Check
XLII = (50 − 10) + 1 + 1 = 42
Sources and notation notes
Meet the symbols
Each tile shows a sign and what it means. A sign can stand for a whole amount, such as 10 or 100.
- I = 1
- V = 5
- X = 10
- L = 50
- C = 100
- D = 500
- M = 1,000
How the symbols fit together
Put an allowed smaller sign before a larger one: subtract
In IV, the I comes before the V: 5 − 1 = 4. Changing the order changes the number.
Only these six pairs subtract
IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900. For example, use IX for 9; IL is not a valid way to write 49 in this convention.
Repeat signs to add their values
III = 1 + 1 + 1 = 3. Repeat I, X, C, or M at most three times in a row. V, L, and D do not repeat in this convention.
Read the pairs, then add the groups
XLII has XL = 50 − 10 = 40, then I + I = 2. Together: 40 + 2 = 42.
The supported modern convention is 1–3,999. Additive inscriptional variants such as IIII and large-number overbars are outside this renderer. There is no zero sign.
History
Roman numeral conventions developed over centuries and varied in inscriptions, manuscripts, and later printing. They remain visible on clocks, monuments, and numbered volumes. This converter uses the common modern subtractive convention, a standardized selection from that wider historical practice.
How to read it
Read Roman numerals in small groups. Most signs add, but a few specific pairs mean subtraction.
- Learn the sign values: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1,000.
- Look for these pairs first: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, and CM = 900. In each pair, take the smaller value away from the larger.
- For XLII, read XL together: L is 50 and X is 10, so this pair means 50 − 10 = 40.
- The two remaining I signs add one each. Add 40 + 1 + 1 = 42. For MCMXCIV, the groups are M, CM, XC, IV: 1,000 + 900 + 90 + 4 = 1,994.
Limits
The supported modern convention is 1–3,999. Additive inscriptional variants such as IIII and large-number overbars are outside this renderer. There is no zero sign.
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