To say ‘as much as possible’ or ‘as much as you can’ in Japanese, we take the standard potential form of the verb (usually the verb ‘to do’: できる) and add だけ.
できるだけ早く来てほしい。
I want you to come as quickly as possible.
東京の観光地についてできるだけ情報を集める。
Gather as much information as possible about tourist spots in Tokyo.
環境を意識して、できるだけエネルギーを効率的に使うようにする。
Be environmentally conscious and use energy as efficiently as possible.
Using Other Verbs (Verb Repetition)
We can form this phrase using the potential form of verbs other than ‘to do’ (する). Critical Rule: When doing this, you must repeat the action verb immediately after だけ. The structure is: 【Verb: Potential】だけ【Verb: Dictionary/Past】.
彼は昨日の飲み会でお酒を飲めるだけ飲んだみたいなので、今日は二日酔いで来られない。
It seems he drank as much as he possibly could at yesterday’s drinking party, so he can’t come today because of a hangover.
バイキングだから、食べられるだけ食べてくださいね。
It’s an all-you-can-eat buffet, so please eat as much as you can.
As Much As You Want (〜たいだけ)
Using the exact same repetition rule, you can swap the potential verb for the 〜たい (want to) form to mean “as much as you want.”
今日は泣きたいだけ泣いてもいいよ。
It’s okay to cry as much as you want to today.
JLPT Synonym: なるべく
For JLPT N4 and N3, it is highly recommended to learn the adverb なるべく. It is completely interchangeable with できるだけ and is extremely common in daily Japanese.