# What are Roman Numerals? - Number Conversion & Chart

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• 0:00 Definition
• 0:36 Rules
• 1:12 Chart
• 2:00 Converting
• 3:07 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

In this lesson, learn what Roman numerals look like and the rules for converting any number to a Roman numeral. Also, find a handy reference chart you can use for your conversions.

## Definition

Roman numerals are the counting symbols used by the ancient Romans. They used only a few letters from the alphabet. We know these letters as I, V, X, L, C, D, and M. Each letter stands for a certain number. Letters were combined to produce a whole number. When letters are combined, they are either being added or subtracted based on the rules of Roman numerals. We will talk about those rules later. For now, let me show you what numbers these letters stand for:

I V X L C D M
1 5 10 50 100 500 1000

## Rules

When writing Roman numerals, there are only three simple rules you have to keep in mind.

1. You can put the same symbol together up to three times. You can't have four of the same symbols all together. The limit is three.
2. Add from left to right if the symbols are the same or smaller as you go to the right.
3. If you see a smaller symbol followed by a larger symbol, subtract the smaller from the larger.

Using Roman numerals can really hone your addition skills. It might seem difficult now, but it gets easier with practice.

## Chart

Here is a handy reference chart you can use for common numbers. We will talk about how to convert in the next section.

I II III IV V VI VII VIII IX
1 2 3 4 5 6 7 8 9

X XX XXX XL L LX LXX LXXX XC
10 20 30 40 50 60 70 80 90

C CC CCC CD D DC DCC DCCC CM
100 200 300 400 500 600 700 800 900

Look at the chart, and see if you can see the rules being played out. Do you see how you can have at most only three of the same symbols together? After that, you use the subtraction rule to get to your next number. Notice you use addition for the number 3, and then you use subtraction for the number 4. The same goes for the numbers 8 and 9. One uses the addition rule and the other the subtraction rule because of the limit that exists for using the same symbol in a row. Also, did you notice how the numbers are added from left to right?

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