Facts for Kids

The letter K (uppercase) and k (lowercase) is the eleventh letter in the Latin alphabet. In English its name is called "kay," and the plural is "kays." You see it in words like kite, kangaroo, and book.

Most of the time, K stands for the sharp, popping sound you hear at the start of kite or the end of back. People all over the world use the same shape or similar letters to write this sound in many languages, so K is a small but useful letter in lots of alphabets.

Long ago, the shape and name of K passed through many cultures. The Greek letter kappa gave its look to our K. Before that, people in the Middle East used a letter called kaph that meant an open hand.

Even earlier, an Egyptian picture of a hand helped shape those letters. When the Romans wrote Latin, they kept a K but mostly used C and Q for similar sounds. Over time C and G took over many jobs, so K stayed mostly in a few words and later loanwords.

In English, K usually makes the same hard sound as in kit or clock. But sometimes the K is quiet. When K comes right before the letter N at the beginning of a word, the K is often not spoken, so words like knight, knife, knot, know, and knee start with the N sound. This is called a silent K.

You also get silent K after some prefixes (unknowable) and inside some older compound words (penknife). Overall, K is not one of the most common letters in English — it appears in only a small number of letters written or typed.

Many languages use K to show the same hard sound you hear in English. In Spanish, German, Turkish, and lots of others, K stands for the clear /k/ sound at the start of words like kilo and kilo (same idea in several languages).

When languages borrowed words from Greek, they sometimes used K to stand for the Greek kappa, especially in modern spellings. In some places the sound can be a little different before certain vowels, but K is a reliable way to write the basic "k" sound in alphabets around the world.

Unicode and other computer tables give each letter a number so machines can store and share text. For example, the capital K is number 75 and the small k is number 107 in ASCII, a simple code used long ago and still useful today. Unicode includes those and many more, like a special Kelvin sign (K) and fullwidth K characters used in East Asian text.

Computers turn letters into these numbers, and fonts decide how the letter looks on the screen. When people write web pages they can use number codes (like K for K) or the real character. This helps computers and phones show the right K, even when type styles or languages are different.

K and k appear in lots of places beyond words. In measurements, a small k means "kilo-", which is 1,000 of something (for example, 1 kilometre is 1,000 metres and is written "km"). A big K is also the symbol for the unit of temperature called the kelvin. In chemistry, K stands for the element potassium.

K shows up in games and everyday signs too. In chess, K means the King. In baseball, a K marks a strikeout (a backward K means the batter looked and didn’t swing). In printing, the letter K stands for black ink in CMYK. A white K inside a blue triangle can mean a kosher certificate. People also use K as a short OK in texts, and in Morse code K means "over," or go ahead.

K comes from a long family of letters. A very old letter called Kaph (written 𐤊) was used by people long ago and passed its sound and shape on to other alphabets. From that came the Greek letter kappa (Κ κ), and from kappa came the Latin K we use now and the Cyrillic letter Ka (К к).

Letters are like family members: they change a little as they move to new places and languages. Some cousins look very similar and make the same /k/ sound, while others changed shape or the way they are written. This is why many alphabets have related letters that feel like cousins and ancestors of K.