Japanese uses different counter words depending on what you are counting. Learning the most common counters is essential for everyday conversation.
〜つ
～つ
General objects (1–9)
ひとつone (thing)
ふたつtwo (things)
みっつthree (things)
Use for misc objects when unsure of specific counter
〜本
～ほん/ぼん/ぽん
Long cylindrical things (pens, bottles, rivers)
いっぽんone (pen/bottle)
にほんtwo
さんぼんthree
Sound changes: 1本=いっぽん、3本=さんぼん、6本=ろっぽん
〜枚
～まい
Flat thin things (paper, shirts, tickets)
いちまいone sheet/piece
にまいtwo
さんまいthree
Regular pattern: いち、に、さん + まい
〜冊
～さつ
Books and bound volumes
いっさつone book
にさつtwo books
さんさつthree books
1冊=いっさつ (double consonant!)
〜匹
～ひき/ぴき/びき
Small animals (cats, dogs, fish)
いっぴきone (small animal)
にひきtwo
さんびきthree
1匹=いっぴき、3匹=さんびき、6匹=ろっぴき
〜頭
～とう
Large animals (horses, cows, elephants)
いっとうone (large animal)
にとうtwo
さんとうthree
Used for zoo animals, livestock
〜台
～だい
Machines, vehicles, electronics
いちだいone (machine/car)
にだいtwo
さんだいthree
Cars, TVs, computers, bicycles
〜杯
～はい/ばい/ぱい
Cups, glasses, bowls of liquid
いっぱいone cup/glass
にはいtwo
さんばいthree
1杯=いっぱい also means 'full'!
〜人
～にん (except 1,2)
People
ひとりone person
ふたりtwo people
さんにんthree people
1人=ひとり、2人=ふたり (special!), 3人〜=さんにん、よにん...
〜階
～かい/がい
Floors of a building
いっかい1st floor
にかい2nd floor
さんがい3rd floor
1階=いっかい、8階=はっかい、10階=じっかい