Моя новая квартира больше, чем старая.

My new apartment is bigger than the old one.

Breakdown of Моя новая квартира больше, чем старая.

• мой: my
• новый: new
• старый: old
• квартира: the apartment

Questions & Answers about Моя новая квартира больше, чем старая.

Why is it моя новая квартира, and why do all those words end in -ая?

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.

Why is it больше and not большая?

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.