In short

Japanese measures a degree by illustrating it: instead of “extremely tired” you say 死ぬほど疲れました shinu hodo tsukaremashita, literally “tired to the extent of dying”. ほど hodo points up toward an extreme and is the formal one; くらい／ぐらい kurai / gurai points at an approximation or plays something down. Stack ほど on the ば-form of the last lesson and you get proportion: 考えれば考えるほど kangaereba kangaeru hodo, “the more I think about it, the more…”.

The rule

Step 1 - Degree by illustration: plain form / noun + ほど・くらい. Both behave like nouns (the dictionaries class this use as 副助詞, an adverbial particle), so whatever precedes them must be in the plain form (lesson 17) - never ます, never です. The illustration comes first, the real predicate last:

[illustration in plain form] + ほど／くらい + [adjective or verb]

• 泣きたいほどうれしかったです。 (Nakitai hodo ureshikatta desu.) - I was so happy I could have cried.
• 子供でも分かるくらい簡単な問題です。 (Kodomo demo wakaru kurai kantan na mondai desu.) - It is easy enough that even a child would understand.

English needs “so … that”; Japanese just puts the picture in front of ほど. Note that politeness is carried by the final predicate only. Before a noun, both take の: 泣きたいほどの喜び nakitai hodo no yorokobi (“joy that makes you want to cry”), 子供でも分かるくらいの問題 kodomo demo wakaru kurai no mondai (“a problem even a child could understand”).

Step 2 - ほど aims up, くらい aims down. They are not free variants.

• ほど picks a scale-topping image and is at home in writing and formal speech: 死ぬほど, 信じられないほど shinjirarenai hodo (“unbelievably”), 山ほど yama hodo (“a mountain of”).
• くらい／ぐらい picks an ordinary, low or trivial image, and belongs to everyday speech: 子供でも分かるくらい, 五分くらい.
• Only くらい can belittle something - “no more than that”: それくらい大丈夫です sore kurai daijōbu desu (“that much is fine”), それくらい自分でしてください (“do that much yourself”). ×それほど大丈夫です does not work in this sense.
• With a quantity, both are fine but the register differs: 一時間ほど話しました is formal/written, 一時間ぐらい話しました is what you say out loud. くらい and ぐらい are the same word - the dictionaries list ぐらい as a voiced variant of くらい, and either is acceptable here.

Step 3 - 〜ほど〜ない, revisited. From lesson 31: A は B ほど + negative = “A is not as … as B”. The predicate must be negative.

今年は去年ほど寒くないです。 (Kotoshi wa kyonen hodo samukunai desu.) - This year is not as cold as last year.

At B1, extend it beyond adjectives to whole clauses: 思ったほど難しくなかったです omotta hodo muzukashikunakatta desu (“it wasn’t as hard as I thought”), 期待したほど売れませんでした (“it didn’t sell as well as we hoped”). The より-comparison of lesson 31 states a gap; ほど〜ない denies that a level was reached, which is softer and less blunt.

Step 4 - Proportion: 〜ば〜ほど. Repeat the same word twice - once in the ば-form from lesson 51, once in the plain form before ほど:

V-ば + V-dictionary + ほど / A-ければ + A-い + ほど

高ければ高いほど、よく売れます。 (Takakereba takai hodo, yoku uremasu.) - The more expensive it is, the better it sells.

Only ほど builds this - ×高ければ高いくらい is ungrammatical. The ば half may be dropped in casual speech (考えるほど分からなくなる), but write it in full while you are learning. For な-adjectives the second half keeps its な: 静かなら静かなほど. For nouns, use the であれば pattern: プロであればあるほど puro de areba aru hodo (“the more of a professional you are…”).

Step 5 - Parallel change without a conditional: 〜につれて and friends. These need no ば-form at all. Most of them take a dictionary-form verb or a noun, and they describe two things changing together over time.

• 〜につれて ni tsurete - the neutral default, gradual and natural: 時間が経つにつれて〜
• 〜にしたがって ni shitagatte - slightly formal; the second change follows the first, as if obeying it: 山を登るにしたがって〜
• 〜とともに to tomo ni - written and formal, “together with”; also plain simultaneity.
• 〜に伴って ni tomonatte - written, news register; a large change brings a consequence with it. This one prefers a noun: 人口の増加に伴って〜 - a verb attaches in its dictionary form, 人口が増えるに伴って, or nominalised with の: 人口が増えるのに伴って.

Two restrictions worth memorising: the change must be gradual and continuous (not a single event), and the main clause must be a description, not a request or an intention - ×暖かくなるにつれて、旅行しましょう is wrong; use たら for that.

Step 6 - Reinforcing adverbs. だんだん dandan, どんどん dondon and ますます masumasu sit in the main clause and make the movement audible: 練習すればするほど、どんどん上手になります。They are optional but very natural in these patterns.

Step 7 - Fixed extent: できるだけ / なるべく. できるだけ dekiru dake (“as much as one can”) and なるべく narubeku (softer, mostly with requests) go straight in front of the adverb, adjective or verb they limit: できるだけ早く, なるべく静かに. Treat them as single words, not as productive grammar.

Forms & patterns

ほど vs くらい／ぐらい.

Building 〜ば〜ほど by word class.

Parallel change: which one to use.

Reinforcing adverbs.

Examples

Common mistakes

• 考えるば考えるほど分からなくなります。 (Kangaeruba kangaeru hodo wakaranaku narimasu.) -> 考えれば考えるほど分からなくなります。 (Kangaereba kangaeru hodo wakaranaku narimasu.) - the first half must be a real ば-form, built on the -e- row: 考えれば, 読めば. ば never attaches to the dictionary form.
• 静かなら静かほどいいです。 (Shizuka nara shizuka hodo ii desu.) -> 静かなら静かなほどいいです。 (Shizuka nara shizuka na hodo ii desu.) - ほど is a noun, so a な-adjective in front of it keeps its な, exactly as in 静かな部屋.
• 大阪は東京ほど大きいです。 (Ōsaka wa Tōkyō hodo ōkii desu.) -> 大阪は東京ほど大きくないです。 (Ōsaka wa Tōkyō hodo ōkikunai desu.) - 〜ほど in a comparison demands a negative predicate. With an affirmative it is simply ungrammatical; for an affirmative gap use より.
• 時間が経ったにつれて、痛みは軽くなりました。 (Jikan ga tatta ni tsurete, itami wa karuku narimashita.) -> 時間が経つにつれて、痛みは軽くなりました。 (Jikan ga tatsu ni tsurete, itami wa karuku narimashita.) - につれて takes the dictionary form or a noun. The た-form turns a gradual process into a finished event, which the pattern cannot express.
• 泣きたいですほどうれしかったです。 (Nakitai desu hodo ureshikatta desu.) -> 泣きたいほどうれしかったです。 (Nakitai hodo ureshikatta desu.) - the clause in front of ほど is a modifier, so it stays plain. Politeness belongs to the final predicate only.

Tips

• Japanese states degree with a picture, not an intensifier. Where English piles on “extremely, incredibly, terribly”, Japanese names a limit and adds ほど: 死ぬほど暑い, 信じられないほど安い, 山ほどある. Collecting five of these images buys you more expressive range than any list of adverbs.
• Up = ほど, down = くらい. ほど reaches for the ceiling and sounds formal; くらい shrugs and sounds casual. That single axis predicts almost every choice, including why それくらい大丈夫です (“it’s only that much”) can never be それほど.
• ば〜ほど is one word repeated twice. Say the word, bend it into ば, say it again plain, then ほど: 高い -> 高ければ高いほど. If the two halves are different words, you have built something else.
• につれて is not a conditional. It describes, so it cannot end in ましょう, てください or つもりです. If your main clause is a plan or a request, you want たら or ば instead (lesson 24).
• Coming later: 〜くらいなら (“rather than…”), as in 待つくらいなら歩いて行きます matsu kurai nara aruite ikimasu (“rather than wait, I’ll walk”). It is built from these pieces but belongs to the B2 band - recognise it, don’t drill it yet.