Roman numerals rules and examples

This page explains how standard Roman numerals are built for whole numbers from 1 to 3999. Use it alongside the Roman numerals converter on the homepage when you want a quick lookup.

What are the seven basic symbols?

I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1000. Most numbers combine these letters. Read from left to right and add each value unless a smaller symbol comes just before a larger one.

When do you subtract instead of add?

Subtractive notation uses a smaller symbol directly before a larger one. Common pairs are IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). Only I, X, and C may be used this way, and only in front of the next two larger symbols in the list (I before V or X, X before L or C, C before D or M).

How often can a symbol repeat?

The same symbol may appear up to three times in a row (III = 3, XXX = 30). Four identical letters in a row are not used in the standard form taught for modern dates and chapter numbers. If you are unsure about a long string, check it with the converter.

Worked examples you can verify

Open these sample conversions on the site: IV (4), XLIX (49), 2026 (MMXXVI), and 3999 (MMMCMXCIX). Each link shows both the Roman form and the decimal value on its own result page.

Where are Roman numerals still used?

You will see them on clock faces, book chapters, film sequels, monarch names, and building cornerstones. They are not used for everyday arithmetic today, but they remain a fixed notation for labels and years when a classic style is wanted.

Enter any value in the form below to jump straight to its conversion page.