atusa ga taisetu desu.

厚さ means thickness.

It comes from the adjective 厚い, which means thick, and turns it into a noun meaning thickness or the degree of thickness.

So in this sentence, 厚さ is the thing being talked about: thickness.

The さ is a very common way to turn an i-adjective into a noun that expresses a quality or measurement.

So:

• 厚い = thick
• 厚さ = thickness

This is similar to English patterns like:

• high → height
• deep → depth
• long → length

More Japanese examples:

• 高い → 高さ = height
• 長い → 長さ = length
• 広い → 広さ = width / spaciousness

So 厚さ is literally the thick-ness.

が marks 厚さ as the grammatical subject of the sentence.

So:

• 厚さが = thickness is / thickness does...

Then the sentence says:

• 大切です = is important

So the full structure is:

• 厚さが大切です = Thickness is important

In simple terms, が is marking the thing that is important.

A learner may wonder whether は could be used instead. It could, depending on context, but it would change the nuance:

• 厚さが大切です = thickness is important
• 厚さは大切です = as for thickness, it is important

が is very natural when identifying what matters.

Yes, 大切 is what is usually called a na-adjective.

That means it behaves differently from an i-adjective like 厚い.

Examples:

• 大切です = is important
• 大切な本 = an important book

Notice that before a noun, it needs な:

• 大切なこと = an important thing / an important matter

But at the end of a sentence, it can go directly before です:

• 大切です = is important

So in this sentence, 大切です works as the predicate: is important.

Because な is only used when a na-adjective comes directly before a noun.

For example:

• 大切な本 = an important book

But in 厚さが大切です, 大切 is not modifying a noun. It is finishing the sentence as the main description.

So:

• 大切な
  • noun
• 大切です at the end of a sentence

That is why な does not appear here.

です makes the sentence polite.

So:

• 厚さが大切だ = plain style
• 厚さが大切です = polite style

It does not add a new meaning like tense or emphasis here; it mainly affects politeness and tone.

This is the normal form you would use in neutral polite conversation, explanations, or writing aimed at learners.

Yes, very possibly.

Japanese often leaves out information that is understood from context. So 厚さが大切です by itself means Thickness is important, but in real use it often implies something like:

• For bread, thickness is important.
• When choosing a mattress, thickness is important.
• In this recipe, thickness is important.

Japanese does not always say all of that if the listener already knows what is being discussed.

So this sentence can sound a little broad in English, but in Japanese it is completely normal if the context is already clear.

Yes, 厚さは大切です is possible, but the nuance is different.

Very roughly:

• 厚さが大切です focuses on thickness as the thing that is important.
• 厚さは大切です sets thickness up as the topic: As for thickness, it is important.

A simple way to think about it:

• が often answers what is important?
• は often means speaking of thickness...

Without a larger context, が sounds very natural here.

Both 厚さ and 厚み can relate to thickness, but they are not always used in exactly the same way.

• 厚さ often sounds more neutral, measurable, or objective.
• 厚み can sometimes sound a bit more physical, substantial, or qualitative.

For many beginner situations, it is safest to learn:

• 厚さ = thickness

So 厚さが大切です is a very straightforward way to say Thickness is important.

No, standard Japanese normally does not use spaces between words.

This sentence would usually be written as:

• 厚さが大切です。

Spaces are often added in beginner materials to make the structure easier to see:

• 厚さ | が | 大切 | です

So the spaced version is for learning convenience, not normal Japanese writing.

It is pronounced:

• あつさ が たいせつ です

Word by word:

• 厚さ = あつさ
• が = ga
• 大切 = たいせつ
• です = desu

In careful pronunciation, です is often said a little like des, with the u becoming very light in everyday speech. But as a learner, saying desu clearly is perfectly fine.