Convert the letter "I" to the number 1. One I equals 1, two I letters equals 2 and three equals the number 3. If you have an I to the left of another Roman numeral letter, subtract one from that value.
Convert the letter "V" to the number 5. If you see "IV," it means 4 because the I on the left of the V means to subtract 1. If you see "VI," it means 6. You write 7 as "VII" and 8 as "VIII."
Convert the letter "X" to the number 10. Translate "IX" as 9, as the I is to the left of the X.
Convert letters using I, V and X in the same manner for numbers 1 through 39.
Convert the letter "L" to the number 50, the letter "C" to the number 100, the letter "D" to the number 500 and the letter "M" to the number 1,000.
Convert higher numbers using combinations of letters using the same logic that a lesser letter to the left means to subtract and a lesser letter to the right means to add. For example, you would convert "XL" as 40 because you have 50 minus 10. Another example is "DC," which you would convert to 600 because you have 500 plus 100.