Моя новая квартира больше, чем старая.

Because квартира is a feminine singular noun.

In Russian, adjectives and possessives must agree with the noun they describe in gender, number, and case.

So:

• моя = my for a feminine singular noun
• новая = new for a feminine singular noun
• квартира = apartment / flat

If the noun were masculine, the forms would change. For example:

• мой новый дом = my new house

So the -ая ending here shows feminine singular nominative.

Because больше is the comparative form of big / larger, while большая is just the normal adjective big in feminine singular form.

Compare:

• большая квартира = a big apartment
• квартира больше = the apartment is bigger

So in your sentence:

• Моя новая квартира больше... = My new apartment is bigger...

Russian often uses the comparative form directly, without a separate word for more.

In the present tense, Russian usually does not use a verb meaning is / am / are.

So:

• Моя новая квартира больше literally looks like My new apartment bigger
• but it means My new apartment is bigger

This is completely normal in Russian.

If you wanted past or future, a form of быть would appear:

• Моя новая квартира была больше = My new apartment was bigger

Here чем means than in a comparison.

So:

• больше, чем... = bigger than...

This is one of the most common ways to make comparisons in Russian.

Example:

• Анна выше, чем Мария. = Anna is taller than Maria.

So in your sentence:

• Моя новая квартира больше, чем старая. = My new apartment is bigger than the old one.

Because Russian often omits a noun when it is obvious from context.

Here, старая really means:

• старая квартира = the old apartment

But since квартира was already mentioned earlier, Russian leaves it out:

• Моя новая квартира больше, чем старая.

English does the same sometimes:

• My new apartment is bigger than the old one.

So старая is standing in for старая квартира.

Because it still refers to квартира, even though the noun is omitted.

The hidden full phrase is:

• чем старая квартира

Since квартира is feminine singular, the adjective must also be feminine singular:

• старая

If the hidden noun were masculine, it would change:

• Мой новый дом больше, чем старый.
• My new house is bigger than the old one.

Yes. Квартира usually means apartment in American English or flat in British English.

It refers to a dwelling in a larger building, not a detached house.

A few related words:

• квартира = apartment / flat
• дом = house / home / building, depending on context
• комната = room

So моя новая квартира is naturally my new apartment or my new flat.

Yes, Russian word order is more flexible than English, but the basic sentence you have is the most neutral and natural:

• Моя новая квартира больше, чем старая.

You might change word order for emphasis, but not every version sounds equally natural in every context.

For example:

• Новая моя квартира больше, чем старая is possible, but marked and less neutral.
• Моя квартира новая means something different in focus: My apartment is new.

For learners, it is best to keep the standard order:

• possessive + adjective + noun + comparative

Yes, in standard Russian writing, a comma is normally used before чем in this kind of comparison:

• Моя новая квартира больше, чем старая.

This is the usual written form.

In speech, of course, you do not hear a comma, but there is often a slight pause.

It is pronounced approximately like BOL-she.

A more helpful breakdown:

• бо = like bo in bore, but shorter
• ль = a soft l
• ше = she

So:

• больше ≈ BOL-she

The л is soft because of the ь. That softness is important in Russian pronunciation.

Yes. Russian has another common comparison pattern:

• больше, чем старая
• больше старой

Both can mean bigger than the old one.

The difference is grammatical:

• чем старая keeps the adjective in the same nominative-style form because the noun is understood
• старой is in the genitive case after the comparative

For a learner, больше, чем старая is often easier to understand at first, because it matches the idea than the old one more directly.

No. Больше can mean bigger, larger, or more, depending on context.

Examples:

• квартира больше = the apartment is bigger
• денег больше = there is more money
• времени больше = there is more time

In your sentence, because it is about an apartment, the meaning is clearly bigger / larger in size.

You would say:

• Моя новая квартира меньше, чем старая.

Here:

• меньше = smaller / less

This is parallel to больше:

• больше = bigger
• меньше = smaller

So it is a very useful pattern to learn.