How can I express that X is as big/small/fast/... as Y?

Question

I would like to know how to express that something is equal in some aspect to another thing (or person, if that makes a difference), as you would express in English by saying:

X is as (adjective) as Y

for example: This car is as fast as that car.

It would also be interesting for me to learn how to say:

"is not as (adjective) as" "is nearly as (adj) as" "can/might/will be as (adj) as" "want to be as (adj) as"

Thank you very much for your help!

Answer 1

In addition to くらい／ぐらい as @rintuan mentioned, ほど (meaning "extent" or "limit") is your friend:

X is not as (adjective) as Y　→　ほど〜ない

• あの少年はお兄さんほど背が高くない　→　That boy is not as tall as his older brother.
• 生物学は物理学ほど面白くない　→　Biology is not as interesting as physics.

Other comparisons: "to the extent of 〜"

• 今日はセーターを着るほど寒い　→　Today is cold enough to (need to) wear a sweater; "Today is cold to the extent of wearing a sweater"

Some other alternatives:

Two things being nearly equal in some aspect

• この車とあの車と、速さはだいたい同じ　→　This car is about as fast as that car; "As for this car and that car, their speeds are about the same"
• ねこくらいの大きさのネズミ　→　A rat (about) as big as a cat

Answer 2

Exactly what you're looking for...

One phrase which I believe will help you is 「～と同【おな】じくらい～」. This literally means "to the same degree as" and seems like it will fit what you're asking for. Some examples:

• 耳【みみ】が顔【かお】と同じくらい大きい。 His ears are as big as his face.
• モデルと同じくらいかわいい。 She is as cute as a model.

This form will with with i-adjectives, but with na-adjectives, you'll need to use に, e.g.:

• ちっちゃい魚【さかな】もおっきい魚と同じくらいに[上手]{じょうず}に泳【およ】ぐよ。 Small fish swim just as well as big fish.

...And a [better?] alternative

Of course, you might also consider using 「～のように～」. It doesn't capture exactly the same nuance, but I think it does well enough. It also has the benefit of sounding much more natural in many scenarios. For example:

• 輝【かがや】く瞳【ひとみ】は星【ほし】のようにきれい。 Your shining eyes are beautiful like the stars.

Extending the meaning

Both of these phrases are equally versatile when you want to extend their meanings. You mentioned "not as", "can/might/will be as", and "want to be as"... all of these are possible by doing what you'd normally do in Japanese to say these things.

• モデルと同じくらいかわいくなりたい。 I want to be as cute as a model. [Note: It's true! I do!]
• 耳【みみ】が顔【かお】と同じくらい大きくなるだろう。 His eyes will probably be as big as his face.
• 人【ひと】は魚と同じくらいに[上手]{じょうず}に泳【およ】げないよ。 A person can't swim as well as a fish.

And just in case you really want your girlfriend to break up with you:

• 瞳【ひとみ】は星【ほし】のようにきれいじゃない。 Your eyes are not beautiful like the stars.

_{Note: basis for example sentences sourced from various Japanese-language websites.}