Ever seen a XVI or XCV label on something and been totally confused? You're probably not alone, as the Roman numeral system is taught and used less and less these days.
In recent centuries, pretty much the entire world has transitioned over to the modern numeral system (also known as Arabic or Hindu-Arabic numerals), which uses 10 symbols (numbers 0 through 9) to make up all other numbers.
However, before that system emerged, one of the primary numeral systems was created by the Romans. Unlike many other ancient systems, Roman numerals are still in use today, albeit in a limited capacity. Let's explore how we use Roman numerals and beyond in our everyday lives.
What Is the Roman Numeral System?
The Roman numeral system is an ancient method of writing numbers that uses combinations of letters from the Latin alphabet to signify different values.
Seven basic symbols — I, V, X, L, C, D and M — stand for the numbers 1, 5, 10, 50, 100, 500 and 1,000. Numbers are formed by combining these symbols and adding their values together, and sometimes they are subtracted; for example, IV for 4.
The ancient Romans developed their numeral system to meet the needs of daily commerce and administration. Even without a positional numerical system or a zero, Roman numerals provided a practical way to record transactions, keep track of census data, label military units and mark milestones.
Basic Roman Numeral Rules
Even though they're called "numerals," they're actually what we consider to be modern letters (I, V, X, L, C, D and M). Each one has a different value:
1 = I
20 = XX
100 = C
2 = II
30 = XXX
500 = D
3 = III
40 = XL
1000 = M
4 = IV
50 = L
5 = V
60 = LX
6 = VI
70 = LXX
7 = VII
80 = LXXX
8 = VIII
90 = XC
9 = IX
10 = X
From there, Roman numeral users must follow a set of basic rules for combining the seven basic symbols to represent modern numbers:
Addition: If a smaller numeral is placed after a larger numeral, add their numerical values. For instance, VI equals 6 (5 + 1).
Subtraction: If a smaller numeral is placed before a larger numeral, subtract the smaller value from the larger. For example, the Roman numeral XL equals 40 (50 – 10).
Repetition: A numeral can be repeated up to three times in succession to increase its value. Example: III equals 3.
Non-repetition: To prevent four repetitions, a smaller numeral preceding a larger numeral indicates subtraction. Hence, 40 in Roman numerals is XL, not XXXX.
Subtractive notation: Only one smaller numeral may precede a larger numeral, and it should be either 1/5 or 1/10 of the larger numeral's value (I before V or X, X before L or C, etc.).
Descending order: Write numerals in descending order from left to right. For instance, 16 is XVI.
Sequential writing: For numbers like 18, write each numeral in decreasing order (XVIII), but for 19, use subtractive notation for the part after the ten (XIX, not XVIIII).
Converting Roman Numerals to Numbers
It might seem tricky at first, but it's relatively easy to translate these ancient figures into today's numeric system. Here's how to figure out the numerical value of these Latin letters:
List the values. Write down the value for each Roman numeral.
Start from the left. Begin with the leftmost numeral and work your way right.
Add or subtract. If a numeral is followed by one of equal or lesser value, add the values. If it is followed by a larger one, subtract it from the larger value.
Combine results. Combine the added and subtracted values to get the total.
Convert Roman Numerals With an Example
Now let's take a crack at converting some Roman numbers. Say you want to convert MCMXLIV.
Start with M (1,000).
Then, subtract C (100) from the following M (1,000), making 900.
Add this to the initial M to get 1,900.
Next, subtract X (10) from L (50) for 40
Add this to 1900 to get 1940.
Subtract I (1) from V (5) for 4
Add that 4 to the previous total for the final number of 1944.
Modern Applications for Roman Numerals
Roman numerals are still used today in various contexts, such as clockfaces, book chapter headings and the numbering of significant sporting events. Clockfaces often use Roman numerals to denote the hours, with the number four typically represented as "IIII" instead of "IV" for aesthetic balance and tradition.
You'll also find people writing Roman numerals quite a lot to indicate succession order, particularly with popes, kings and queens. It'd be pretty weird to modernize Henry VIII to Henry 8, right?
But you don't have to be royalty to enjoy that honor. Any old person can be John Smith, IV, for example, provided three other John Smiths preceded him in the family line.
Another common use for Roman numerals is for competitions, like the Super Bowl and the Olympic Games. Wars, like WWI and WWII, also use Roman numerals to distinguish them, and often monuments and buildings are engraved with the Roman numeral version of the year they were built. Filmmakers do the same thing for copyright dates at the end of film credits.
Limitations and History of Roman Numerals
When you take a look at the Roman numeral system, you may notice that something is missing: the zero. In fact, one of the primary reasons the Roman system became less relevant is that there's no way to denote zero. In mathematical calculations, this is a pretty big problem.
Don't be too hard on the creators of this system, however. It was developed during the early days of ancient Rome. So, things have clearly changed quite a bit, and people had to roll with the times and adapt as needed.
For example, as the study of mathematics progressed, it became obvious that Roman numerals weren't the best for division, multiplication or expressing fractions. This necessitated a shift to a numerical system that could better accommodate these needs, leading to the eventual predominance of the Arabic numerals that we use today.
Still, it's important to know the basics about Roman numerals. Although it's unlikely that you'll ever do math using them, it's likely that you will read books, clocks or watch the occasional Super Bowl.
This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.
Now That's Interesting
Wondering why the Super Bowl, which is a relatively modern Western event, would use Roman numerals? There's some method behind the madness, as it turns out. The league started using Roman numerals because the Super Bowl is played after the start of the new calendar year but is the crowning championship game for the season that started in the previous year. By using Roman numerals, it makes it easier for people to say that a certain team won Super Bowl XL, or whatever, without bringing the year into question.
Original article: VII, MCM, XL: Roman Numerals Made Understandable
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