The number "IV" is the Roman numeral of the number four. In the Roman number notation system, "I" is the equivalent of the number one in the Hindu-Arabic numbering system, and "V" is the equivalent of the number five. This numbering system is still used in certain applications in the world.

**What are Roman Numerals?**

Roman numerals are part of the numbering system used by ancient Romans. Instead of the numbers commonly used today, they relied on letters to represent numbers. This was the standard number notation used throughout Europe during the Middle Ages, and they used it for nearly two millennia before converting to the Hindu-Arabic number notation.

This numerical notation uses the symbols I, V, X, L, C, D, and M in place of the Hindu-Arabic numbers 1, 5, 10, 50, 100, 500 and 1000. These symbols represent larger numbers when a bar is placed over them. For example, a bar over the letter X denotes the number 10,000. There is no symbol for zero in this system, as this was a contribution from Arabic mathematicians.

**S****tandard vs. Alternative Forms of Roman Numeral**

In the standard form of Roman numerals, each number has a fixed value. The letter combinations must be added and subtracted following the traditional rules. In one alternative form of Roman numerals, users add symbols together. For example, the number 9 in standard Roman numeral format is IX.

In addition to the standard form of Roman numerals, there were alternative forms that did not follow all of the standard rules. For example, it's not uncommon to find the number 9 written as XIIII instead of IX. Another alternative form leaves out the letters V and L. In that case, the number 5 is written as IIIII.

**M****odern Uses for Roman Numerals**

People stopped using Roman numerals in everyday life in the fourteenth century as the more efficient Hindu-Arabic numbering system grew more popular. However, it is still common to see Roman numerals in other domains like royal titles, on watches and clocks, buildings, and in entertainment. Publishers sometimes separate chapters in books with Roman numerals, and musicians use them to indicate major and minor triads.

**Adding and Subtracting Roman Numerals**

It's important to note the position of the letters when adding and subtracting Roman numerals. When a letter appears after a larger or equal symbol, you add the numbers. For example, in the combination VI, the value of I is smaller than the value of V. You then add one to five, which equals six. The opposite is true for subtraction. IX is nine. Since the value of I is smaller than the value of X, you subtract one from ten, which equals nine.

**H****ow to Use a Roman Numeral Conversion Tool**

Sometimes trying to sort through the numbers to add and subtract them is cumbersome. That's when people may rely on a Roman numeral conversion tool to do the calculations for them. They enter the series of Roman numerals and let the tool convert them to more recognizable Hindu-Arabic numbers.