～つ

～つ counts ordinary things, from one to ten. The numbers in front of it are not いち, に, さん but an older Japanese set, so each form is learned as a word.

Number	Written	Reading
1	一つ	ひとつ
2	二つ	ふたつ
3	三つ	みっつ
4	四つ	よっつ
5	五つ	いつつ
6	六つ	むっつ
7	七つ	ななつ
8	八つ	やっつ
9	九つ	ここのつ
10	十	とお

The number usually comes after the noun and its particle, straight in front of the verb, with no particle of its own.

Four of the readings have a small っ: みっつ, よっつ, むっつ, やっつ. Ten is とお, with no つ at all.

Asking how many

The question word is いくつ, built on the same つ.

What it counts

～つ counts objects that have no special counter, or whose counter you don't know: apples, cakes, chairs, bags, boxes. It also counts things that are not objects at all, such as questions and problems, and it works for giving numbers when ordering.

People and animals are not counted with ～つ; they have counters of their own.

Common mistakes

×いちつ, ×につ and ×さんつ are wrong. The forms are ひとつ, ふたつ, みっつ. ×とおつ is wrong as well.

A number in front of the noun needs の. ×二つりんごを買いました is wrong.

Usage notes

These go beyond counting things from one to ten.

Age

いくつ also asks how old someone is, and a small child's age is often given with ～つ.

Past ten

～つ stops at ten. From eleven on, use the ordinary number, alone or with the counter こ個: eleven things are じゅういち十一 or じゅう いっこ十一個.