Suffixes “st”, “nd”, “rd”, and “th”

When we use numbers with letters after them, we might come across symbol endings like “st,” “nd,” “rd,” and “th.” These are known as ordinal indicators, and it would help to know how they work. This article will explain all you need to know.

What Do “st,” “nd,” “rd,” And “th” Mean?

“St,” “nd,” “rd,” and “th” are suffixes that we can include at the end of a number. They allow us to turn words like “One” into “first,” “two” into “second,” and “three” into “third.” They are used to create lists or orders of how things might have happened.

It’s most common to see these suffixes when we are using the numerical form.

For example, we would see it apply to the following:

Every number between 4 and 20 uses the “th” suffix after it. Only 1, 2, and 3 have different suffixes, and each one is independent of themselves or any extension of 1, 2, or 3 (i.e. 21, 32, and 43).

Words With “st,” “nd,” “rd,” and “th”

While it’s most common for us to see these suffixes used for numerical values, the same numerical values can be written out in the long form.

1st: First
2nd: Second
3rd: Third
4th: Forth

As you can see, the extensions and suffixes are always kept the same. The only thing that changes is the spelling of the word (which acts as a prefix). 1 becomes “fir-,” 2 becomes “seco-,” and so on.

What Are “st,” “nd,” “rd,” And “th” Called?

These suffixes are officially known as ordinal indicators. They work after numbers because they allow us to create lists or orders of how things works. “St,” “nd,” and “rd” are all specific to the numbers 1, 2, and 3, respectively. “Th” is for the other numbers between 4 and 20.

You’ll more than likely come across the ordinal indicator “th” since it applies to many more contexts.

It’s also possible to see them written in superscript, which means the letters are shifted up to the top of the number, like so:

1^st
2^nd
3^rd
4^th

There are no specific rules that dictate whether superscript should be used or not. Instead, it mainly depends on personal preference.

You’ll often find that more formal publications will use superscript with their ordinal indicators because it helps to establish the differences between the letters and the numbers.

When Were “st,” “nd,” “rd,” And “th” First Used?

Ordinal indicators were first used during the reign of the Roman Empire. They were used with Roman numerals like V and X rather than the traditional numbers that we’ve come to learn about today. In Roman numerals, ordinal indicators were always written in superscript.

So, thousands of years ago, you might have seen these numbers indicated like so:

XX^o

They allowed Romans to create lists or orders of how things happened. The usage hasn’t changed much today.

However, at some point during the 20th century, ordinal indicators began to lose their superscript status. It was no longer common for people to write “st,” “nd,” “rd,” or “th” above the letter. Instead, it was written next to it.

One of the most obvious reasons for this came when computers and word processors were created. It made it much harder for people to write in superscript since they would have to repeatedly go back and change the way they wanted to write the letters.

At the end of the day, the extra couple of button clicks to get to the superscript format weren’t worth the time. That’s more than likely one of the biggest reasons why the superscript idea is an old-fashioned one.

Proper Usage Of “st”

“St” is the ordinal indicator for 1 or any other number that uses it as a root (besides 11). We can use it after 1 to create “first.”

You will see “st” used like so:

1st
21st
31st
101st

As you can see, it only applies when 1 is the last number in the group. This is because we would say “twenty-one,” “thirty-one,” and “one hundred and one,” respectively.

So, why do we leave 11 out? Well, it comes from the pronunciation of the word.

If 11 was pronounced “ten-one” or “ten and one,” then we would absolutely write 11st. However, it is pronounced as “eleven,” so we cannot use the “st” ending because it would make no sense.

Proper Usage Of “nd”

Just like “st,” “nd” is specific to only one group of letters. You can only use “nd” when working with 2 or any extension of it. Again, this does not apply to 12 because it does not follow the usual 2 rules.

2nd
22nd
32nd
102nd

We can rely on our pronunciation again here to make sure we know how “nd” works.

12 is skipped because it is not pronounced as “ten-two” or “ten and two.” We say “twelve,” which does not give room for the “nd” ending.

Proper Usage Of “rd”

“Rd” is another specific choice. This time, it only applies to 3 and any extensions of it. 13 is again skipped because it follows different rules that make “th” the more suitable choice.

3rd
23rd
33rd
103rd

13 is skipped because it’s a teen number. All teen numbers (14, 15, 16, 17, etc.) have to end with a “th” because that’s how they are easiest to pronounce.

It’s the only case where the 3 rule of “rd” as a suffix is dropped.

Proper Usage Of “th”

“Th” is the most inclusive ordinal indicator. It applies to every number outside of 1, 2, and 3 (and all the extensions of it). We can use this indicator from 4 to 20 without changing it.

After 20, we can then use it at 24 until 30, 34 until 40, and so on for all the remaining numbers. Only the first 3 numbers of every group of 10 are skipped after 20.

4th
5th
11th
12th
13th
24th
35th
106th
107th
198th
200th

We could go on with this one. “Th” is the most versatile ordinal indicator because it works in the most situations.

Martin Lassen

Martin holds a Master’s degree in Finance and International Business. He has six years of experience in professional communication with clients, executives, and colleagues. Furthermore, he has teaching experience from Aarhus University. Martin has been featured as an expert in communication and teaching on Forbes and Shopify. Read more about Martin here.