Before we learn how to count people we must learn to use counters. Counting quantity in Japanese is different from English because we use counters. Technically speaking there are three different types of counters.

   General counters can be used on any noun, except for people and animals. They are used for items that don't have their own counter, their counter is rarely used, or the speaker doesn't remember the counter for the noun they are trying to count.

   1 - hitotsu (一つ)
   2 - futatsu (二つ)
   3 - mittsu (三つ)
   4 - yottsu (四つ)
   5 - itsutsu (五つ)
   6 - muttsu (六つ)
   7 - nanatsu (七つ)
   8 - yattsu (八つ)
   9 - kokonotsu (九つ)
   10 - too (十)

   The counter 10 is often misspelt as tou, this is incorrect.

   8 pens = pen ga yattsu (ペンが八つ)

   All other items have a different counter depending on the item, shape or form. Another type of counter is the ones that are not used alone as words themselves, instead are only used with a number to count items. From the perspective of an English speaker, it's similar to saying 3 bunches, 2 strokes, 8 scoops.

   Finally we have counters that don't change the pronunciation of the number. These counters are words that can be used alone. From the perspective of an English speaker, these counters are similar to 3 hands, 1 toe, 7 doorknobs.

   Nin (人) is the counter that is used for people. People can't be counted with general counters, they require the proper counter.

   1 person = hitori (一人)
   2 people = futari (二人)
   3 people = sannin (三人)
   4 people = yonin (四人)
   5 people = gonin (五人)
   6 people = rokunin (六人)
   7 people = shichinin (七人)
   8 people = hachinin (八人)
   9 people = kyuunin (九人)
   10 people = juunin (十人)

   The formal way to count people is useing the counter mei (名).