When attached to the end of numbers or counters, the noun
当（あ）たり ‘to hit’ will be used as a suffix. In these cases, the meaning is usually translated as ‘per (A)’, or ‘each (A)’. Let’s take a look at some examples.
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一個（いっこ）当（あ）たり5円（えん）で作（つく）ることができます。
We are able to make this for 5 yen each.
一食（いっしょく）当（あ）たりのカロリーは５００ｋCal です。
It has 500 calories per serving.
While the literal meaning of
当（あ）たり is ‘to meet’ (as in ‘to come into physical contact with’), as a suffix,
当（あ）たり has a nuance that is similar to に対（たい）して ‘to be in relation to’. This similarity can be seen in the following:
(A) 当（あ）たり (B) - Regarding (A), (B) equates to it.
(A) に対（たい）して (B) - Regarding (A), (B) equates to it.
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この車（くるま）は一台（いちだい）当（あ）たり１トンあります。
This car equates to 1 ton per vehicle.
一人（ひとり）当（あ）たり5000円（えん）で入場（にゅうじょう）できます。
The price for entry per person equates to 5000 yen.