In order to read Roman numerals, make sure to know what each symbol means, when numbers add or subtract, and how to handle somewhat-larger numbers.
- Know each symbol
In Roman numerals, M equals 1,000, D equals 500, C equals 100, L equals 50, X equals 10, and I equals one.
- Add numbers when bigger is followed by smaller
When a larger number is followed by a smaller number, such as XI, the numbers are added. Thus, XI = 10 + 1 = 11.
- Subtract numbers when smaller is followed by bigger
When it is the opposite, such as IX, the smaller number is subtracted from the bigger number. So, IX = 10 - 1 = 9.
- Use only three of the same symbol together
When using multiple numbers of the same value, no more than three of the same symbol should appear together. If four are needed, it should be that value subtracted from the next-largest value. Examples include XL = 40, IV = 4 and CD = 400.
- Add a bar on top if multiplying by 1,000
For each value above one, placing a bar or vinculum above the number multiplies it by 1,000. For instance, an X with a vinculum is 10,000.