Translation guide
The number two in Japanese is most commonly expressed as に (ni) in counting and everyday contexts, but the reading changes depending on the counter or classifier used. For the abstract number, に is standard. When counting objects, the native Japanese number ふた (futa) appears in words like ふたつ (futatsu) for 'two things'. In formal or Sino-Japanese compounds, に is used. The choice between に and ふた depends on what is being counted.
Expressing the number two as a numeral, in arithmetic, or when reciting numbers.
Counting two of something when no specific counter is needed, or using the generic counter つ.
Counting two people.
Counting two small animals or creatures using the counter 匹 (ひき).
The counter 匹 is used for small animals. The number two is read as に, and 匹 becomes ひき due to rendaku (voicing) in some contexts, but here it remains unvoiced.
猫が二匹います。
There are two cats.
Counting two of something long and thin, like bottles, pencils, or trees.
The counter 本 (ほん) is used for long, cylindrical objects. The number two is に, and 本 is read as ほん. Note: にほん also means 'Japan', but context distinguishes them.
Counting two flat things like paper, tickets, or plates.
The counter 枚 (まい) is for flat objects. Two is に, and 枚 stays まい.
Counting two bound items like books or magazines.
The counter 冊 (さつ) is for books and magazines. Two is に, and 冊 is さつ.
この本を二冊読みました。
I read two of these books.
Counting two mechanical items like cars or computers.
The counter 台 (だい) is for machines and vehicles. Two is に, and 台 is だい.
In Japanese, you cannot simply say に plus a noun to mean 'two X'. You must use a counter word appropriate to the object. For example, 'two apples' is りんごをふたつ or りんごを二個 (にこ), not 二りんご.
りんごを二個買いました。
I bought two apples.
For children's ages, ふたつ is common, but for formal situations or older people, use 二歳 (にさい).
The native Japanese word for 'two things'. Used with the generic counter つ for inanimate objects, abstract items, or when the specific counter is unknown. Also used for age (two years old) in casual contexts.
りんごをふたつください。
Two apples, please.
あの子はふたつです。
That child is two years old.
The standard counter for two people. Uses the native Japanese reading. Note the irregular reading: 人 is usually にん, but here it is り.
二人で映画を見ました。
We saw a movie together (the two of us).
ペンを二本買いました。
I bought two pens.
切手を二枚ください。
Two stamps, please.
There are two cars.