程(ほど)The more, About, To the extent that, So much… that

くらい (often ぐらい in speech) expresses an approximate degree or extent. It's often used with number + counter expressions (the くらい① form), as in 10分くらいかかった = 'It took about ten minutes.' ほど can be used similarly, but is more formal and carries the nuance of an upper limit—e.g., 10分ほど implies 'about, but no more than ten minutes.'

ほど (sometimes written in kanji as 程) has the basic meaning of 'extent'. ば〜ほど shows a proportional relationship, similar to 'the more (A), the more (B)', e.g. 練習すればするほど上手になる ('The more you practice, the better you get.') When used alone, ほど means 'so much that (A)' or 'to the extent of (A)', e.g. 驚くほど静かだった ('It was quiet to a surprising degree.' / 'It was so quiet that I was surprised.')

Both くらい and ほど can express extent in the sense of 'so much that (A)' or 'to the extent of (A)', and are often interchangeable, e.g. 驚くくらい静かだった / 驚くほど静かだった ('It was quiet to a surprising degree.') くらい (also written as ぐらい) tends to sound slightly more colloquial, and each word has other uses where they may not be interchangeable.

ほど (sometimes seen in kanji as 程) has the basic meaning of 'extent'. ほど〜ない is used for comparisons meaning 'not as (A) as (B)', e.g. 彼ほど背が高くない ('I'm not as tall as him.'). When used alone, ほど means 'so much that (A)' or 'to the extent of (A)', e.g. 驚くほど静かだった ('It was quiet to a surprising degree.' or 'It was so quiet that I was surprised.').

Both relate to expressing extent, but with different emphasis. は～くらいです highlights something as the only or most notable case, like 'about the only (A) is (B)', e.g. できるのは田中さんくらいです ('Mr. Tanaka's about the only person who can do it.') ほど expresses extent or intensity, e.g. 驚くほど静かだった ('It was quiet to a surprising degree.')

まで and ほど both mean 'to the extent of,' but with different uses. まで emphasizes inclusion or a surprising limit, e.g. 骨まで食べた ('He even ate the bones.'). ほど means 'so much that' and often describes degree or intensity, e.g. 痛いほど分かる ('I understand to the point that it hurts.').