In general, the Korean number system can be quite complicated.  What many people don’t realize is that the Korean number system has two distinct number systems.  Each system is used for different purposes.  Sounds complicated right?  Don’t worry, I’m here to help everyone out.  I’ll point out the differences between the two systems, when to use them and the irregularities or pitfalls you need to avoid when using the number system.

Let’s begin with the native Korean numbers.  Native Korean numbers are only used to express numbers 1-99.  It should also be noted that numbers 1-49 are the most commonly used in native Korean numbers.  For example, let’s say that someone asks “몇 살이에요?” (myot saliehyo?)  몇 means how many and 살 (sal) is the counter for age or put in another way it means “years old” while 이에요 (iehyo) is the standard polite ending for nouns ending in a consonant.  Altogether 몇 살이에요 (myot saliehyo) means ‘how old are you?’  Since 살 (sal) is the counter or classifier that requires a native Korean number, you would state your age in native Korean numbers.  If you’re ages 1-49, you’ll probably use the native Korean numbers.  You don’t have to, but most Koreans use the native Korean numbers if they are 1-49 years old.

Let’s say that you’re aged 50-100.  You will most likely use the Sino-Korean numbers instead of the native Korean numbers.  Again, you don’t have to use the Sino-Korean numbers for ages 50-99.  However, most Koreans prefer to use numbers 50-99 with Sino-Korean numbers.  For the number 100 which is pronounced as bek (백), you must use Sino-Korean numbers.  There is no native Korean number equivalent for the number 100.  Also, if you’re going to state your age in Sino-Korean numbers, you have to use the counter or classifer 세 (seh) instead of 살 (sal).

Ok, let’s review everything we learned so far.  When you want to say I’m 15 years old in native Korean numbers you would say 열다섯 살이에요 (yol-dasot sal-i-eh-yo).  However when you want to say I’m 15 years old in Sino-Korean numbers you would say 십오 세예요 (ship-o sehyeyo).  As you’ve noticed, the counter determines whether you use native or Sino-Korean numbers.  The counter for minutes which is 분  (bun) in Korean is always stated in Sino-Korean numbers.  However the counter for hours which is 시 (shi) is always stated in native Korean numbers.  There if you want to say 5 hours and 5 minutes which is another way of saying 5:05, you would say 다섯 시 오 분 (dasot shi o bun). 

So why are there two number systems?  The answer to that is controversial.  Koreans have always had the native Korean number system.  However the Sino-Korean number system was developed later in Korea’s history.  Some say it was imposed upon the Koreans by the Chinese.  Whatever the reason, having two numbers systems can make things quite confusing.  For example, telling time, as shown in the previous paragraph, is no easy feat. 

As a general rule, anything having to do with the calendar, such as the months, days and years are in Sino-Korean numbers.  Anything with objects, such as animals, people, furniture are native Korean numbers.  Initially you’ll have to memorize when to use the Sino-Korean and native numbers, but the more you practice the more intuitive it becomes.