当たりPer unit; per
当たり attaches to a unit and expresses an amount, price, allocation, or average per that unit. It is especially useful for rates such as per person, per day, or per item.
How the rate is built
The unit before 当たり tells you what the amount is measured against. The rest of the phrase supplies or implies what is being measured. For example, a time unit may be followed by a price, while a person unit may be followed by an allocation or a calculated average.
Rates, prices, and allocations
The same structure works for calculated averages, fixed prices, and actual allocations. Context tells you which meaning is intended.
この工場では、一日当たり平均五百個の製品を生産している。
This factory produces an average of 500 products per day.
AnalyzeThis reports a calculated daily average; production does not have to be exactly 500 on every day.
参加者一人当たり、飲料水を二本配ります。
We will distribute two bottles of drinking water to each participant.
AnalyzeThis describes an actual planned allocation, not merely an average.
国民一人当たりの年間医療費を調査した。
Annual medical spending per person was studied.
Analyze当たりの lets the whole rate phrase describe the following noun.
Choosing the right distribution expression
Use 当たり when the central idea is a rate, denominator-based measurement, or average. につき can also express a per-unit relation, but often works as a particle-like frame in notices and stated conditions. ずつ emphasizes actual equal shares or repeated increments. ごとに marks every occurrence or interval and does not itself require a divided amount.
More examples
この地域では、一世帯当たりの電力消費量が昨年より減った。
Electricity consumption per household in this area fell compared with last year.
Analyzeこのコピー機は一枚当たり十円かかります。
This copier costs ten yen per page.
Analyze児童一人当たり三冊のノートを用意した。
We prepared three notebooks for each child.
AnalyzeThis is an actual prepared allocation.
この車は一リットル当たり十八キロ走る。
This car travels 18 kilometers per liter.
Analyzeこの畑では、一平方メートル当たり約四キロのトマトが収穫できる。
About four kilograms of tomatoes can be harvested per square meter in this field.
Analyzeチームの一試合当たりの得点は平均二点だった。
The team averaged two points per game.
AnalyzeThis is a calculated average across multiple games.