Counters: the part nobody warns you about
You cannot just say "three" in Japanese. The word changes with what you are counting.
Japanese does not let a bare number attach to a noun. Counting three pens, three people and three cats uses three different words. The counter goes after the number, and some combinations trigger sound changes.
The counters worth knowing first
General objects, when no specific counter comes to mind. Only goes to 10.
1 ひとつ · 2 ふたつ · 3 みっつ · 4 よっつ · 5 いつつ · 6 むっつ · 7 ななつ · 8 やっつ · 9 ここのつ · 10 とお
People.
1 ひとり (not いちにん) · 2 ふたり (not ににん) · from 3 onward regular: さんにん, よにん, ごにん…
Small round or chunky objects: apples, erasers, stones.
1 いっこ · 6 ろっこ · 8 はっこ · 10 じゅっこ
Long thin things: pens, bottles, umbrellas, trains, phone calls.
1 いっぽん · 3 さんぼん · 6 ろっぽん · 8 はっぽん · 10 じゅっぽん
Flat things: paper, shirts, plates, tickets, SIM cards.
Fully regular. The easiest counter to start with.
Bound volumes: books, magazines, notebooks.
1 いっさつ · 8 はっさつ · 10 じゅっさつ
Small animals: cats, dogs, fish, insects.
1 いっぴき · 3 さんびき · 6 ろっぴき · 8 はっぴき · 10 じゅっぴき
Machines and vehicles: cars, computers, fridges.
Fully regular.
Age.
1 いっさい · 8 はっさい · 10 じゅっさい · 20 はたち (fully irregular, worth memorising on its own)
Yen. Written ¥.
Fully regular: ひゃくえん (¥100), せんえん (¥1,000), いちまんえん (¥10,000).
How it fits in a sentence
The number and counter usually sit just before the verb, not next to the noun. This ordering feels strange at first and then stops being noticeable.
- ねこが三匹います ねこがさんびきいますनेको गा साम्बिकि इमासुThere are three cats
- ビールを二本ください ビールをにほんくださいबीːरु ओ निहोन कुदासाइTwo beers, please
- 学生が四人います がくせいがよにんいますगाकुसेइ गा योनिन इमासुThere are four students