kono setai ha tiisai.

この means this and directly modifies a noun.

So in この世帯, この is attached to 世帯 and means this household.

A useful comparison:

• この + noun = this ...
• その + noun = that ... (near the listener)
• あの + noun = that ... over there

Also compare it with これ:

• これ = this one / this thing
• この世帯 = this household

You cannot say これ世帯. If a noun follows, use この.

世帯 means household: a group of people living together as one unit.

It is a real and common word, but it is a bit more formal or administrative than everyday words like:

• 家族 = family
• うち / 家 = home, household, house

You often see 世帯 in:

• government documents
• statistics
• census data
• news reports
• discussions of taxes, income, or demographics

So the sentence sounds grammatically fine, but the noun 世帯 itself has a slightly formal, factual tone.

It is pronounced せたい.

So the whole sentence is:

この せたい は ちいさい。

Pitch accent can vary by source and dialect, so for most learners the main priority is just remembering the reading せたい.

は marks the topic of the sentence.

In この世帯は小さい, the topic is this household, and the sentence says something about it: that it is small.

A natural way to think about it is:

• As for this household, it is small.

This does not always translate naturally into English word-for-word, but that is the basic function of は.

In Japanese, い-adjectives can act as predicates by themselves.

小さい is an い-adjective, so it can mean is small without needing a separate word for is.

That is why:

• この世帯は小さい。 = This household is small.

By contrast, with a noun or a な-adjective, you would need だ or です in plain/polite style.

Examples:

• この世帯は静かだ。 = This household is quiet.
• この世帯は学生です。 = This household is a student household.
  (This example is a bit odd semantically, but it shows the grammar.)

Because 小さい is an い-adjective, and い-adjectives do not take だ when used normally at the end of a sentence.

So these are correct:

• この世帯は小さい。
• この世帯は小さいです。

But this is incorrect:

• この世帯は小さいだ。

A common learner rule:

• い-adjective → no だ
• noun / な-adjective → usually needs だ / です at the end

この世帯は小さい。 is plain style.

It is not rude by itself, but it is less polite than です style.

Polite version:

• この世帯は小さいです。

Plain style is commonly used in:

• casual conversation
• written explanations
• dictionary examples
• essays
• narration

Because 世帯 is a somewhat formal word, the sentence may feel more like written or factual language than casual everyday speech.

It is understandable, but depending on context, it may sound a little unusual.

Why? Because a household is not physically small in the same way an object is small. A native speaker may wonder what kind of small you mean:

• few people?
• low income?
• small living space?
• limited scale?

Depending on the meaning, Japanese often uses more specific expressions, such as:

• この世帯は人数が少ない。 = This household has few members.
• この世帯は小規模だ。 = This household is small in scale.
• この世帯の住居は狭い。 = This household’s dwelling is small/cramped.

So the original sentence is grammatical, but in real usage a more specific expression might sound more natural.

If you say:

• この世帯は小さい。

you are presenting this household as the topic and saying it is small.

If you say:

• この世帯が小さい。

the nuance changes. が often feels more specific or contrastive, like identifying which one is small.

Possible feeling:

• This household is the one that is small.

So:

• は = topic, general statement about it
• が = stronger focus on the subject itself

In many beginner examples, は is the more neutral choice.

No. Standard Japanese normally does not use spaces between words.

The sentence would normally be written as:

この世帯は小さい。

Spaces are often added in beginner materials to make word boundaries easier to see.

So both represent the same sentence, but the natural written form is the one without spaces.

Yes. 小さい can directly modify a noun:

• 小さい世帯 = a small household

So you can have:

• この世帯は小さい。 = This household is small.
• これは小さい世帯だ。 = This is a small household.

The difference is just sentence structure:

• noun は adjective = the noun is adjective
• adjective + noun = an adjective directly describing the noun

Both are common patterns in Japanese.