くらい / ぐらい

1. 1About or approximately, used after a quantity, number, or length of time.Ex. 1
2. 2To the extent of, or as … as, indicating a degree comparable to something else.Ex. 2

Very common in everyday speech and writing, and neutral in tone. It is used for rough amounts, durations, distances, and prices, and in どのくらい to ask "how much/how long." It also expresses a comparable degree or extent, as in 同じくらい or 驚いたくらい. For an approximate point in time, ごろ is the standard choice, while ほど gives a similar "about" meaning in a somewhat more formal tone.

• ほどN3ほど can also express an approximate amount, in which case it is close in meaning to くらい but slightly more formal; when expressing degree, it is mostly used for high or exaggerated degrees (e.g. 死ぬほど) and cannot express a slight degree like 'just a little'.
• 〜ほど〜ないN5〜ほど〜ない is used only for negative comparison, meaning A falls short of B, and the sentence must end in a negative form; 同じくらい, by contrast, means the two are about the same. For expressing degree, くらい is more colloquial and casual than ほど.
• ごろN5ごろ attaches only to points in time, as in 7時ごろ, and has no usage for degree. When giving an approximate time, ごろ is normally used; it cannot be used for durations or amounts, so 二十分くらいかかります cannot be rewritten with ごろ.
• ばかりN4When attached to a number to express an approximation, ばかり is interchangeable with くらい but less colloquial; ばかり cannot express equal degree the way 同じくらい does, and it has other uses meaning 'nothing but, always' and 'just finished doing'.
• よりN5より marks the standard of comparison and indicates a difference in degree between the two, as in 昨日より寒い; when くらい expresses degree it typically appears as 同じくらい, meaning 'about the same'. より can also mean 'from ...' in formal usage, so the two are not interchangeable.
• だけN5After a number, くらい means 'approximately' while だけ means the restriction 'only, just', so they cannot be swapped: 一杯だけ means 'just one (cup)'. だけ can also express the maximum extent possible, as in できるだけ and 好きなだけ.

ほど also means "about" but sounds more formal, and 〜ほど〜ない means "not as … as"; ごろ marks an approximate point in time rather than an amount, and より marks the standard in a comparison of difference, whereas 同じくらい expresses similar degree. ばかり can also approximate an amount (一時間ばかり "about an hour"), but this use sounds more old-fashioned or literary, and its main use is "only/nothing but"; だけ means "only" and sets a limit rather than approximating.