Learn Finnish: Sinun kokoinen mies tarvitsee vähintään kymmenen grammaa rasvaa. - A man of your size needs at least ten grams of fat.

Both translate to "at least", but vähintään is used for strict numerical minimums and measurements, like the ten grams mentioned here. Ainakin is more subjective and expresses a minimum expectation, relief, or a conversational pivot (e.g., "At least it's not raining"). Because this sentence states an exact limit, vähintään is the natural and correct choice.

How is the word vähintään formed?

It is built from vähin, which is the superlative form of vähän (a little/few). The suffix -tään (or -taan) is used to create adverbs that set a limit or boundary. You can see the exact same grammatical pattern in korkeintaan (at most), which comes from korkein (the highest).

How does the grammar in the phrase sinun kokoinen mies work?

It pairs a genitive word (sinun, meaning your) with an adjective ending in -inen, which is here derived from koko (size). This is a very common Finnish pattern for describing proportions, shapes, or appearances. You will see it in many other everyday phrases, such as saman pituinen (of the same length) or hänen näköinen (looking like him/her).

Why are both grammaa and rasvaa in the partitive case?