La casa és gran.

La is the definite article, meaning the.

So:

• casa = house
• la casa = the house

Catalan uses articles very regularly, often more regularly than English. In a simple sentence like this, la casa is the normal way to say the house.

És is the he/she/it form of the verb ser, which means to be.

So:

• jo soc = I am
• tu ets = you are
• ell/ella és = he/she is

In La casa és gran, és means is.

The accent in és helps distinguish it from es, which is a different word.

• és = is
• es = a reflexive pronoun, like oneself / himself / herself, depending on context

The accent also shows stress and is an important part of correct spelling. So in this sentence, you must write és, not es.

In Catalan, adjectives often come after the noun.

So:

• la casa gran = the big house
• La casa és gran = The house is big

In your sentence, gran comes after és because it is describing the subject through the verb to be. This works much like English The house is big, where big also comes after is.

Gran often means big or large, but it can also mean great or grown-up, depending on context.

Examples:

• una casa gran = a big house
• un problema gran = a big problem
• un germà gran = an older brother

In La casa és gran, the natural meaning is The house is big.

Not all Catalan adjectives change form for masculine and feminine.

Gran is one of those adjectives that usually has the same form for both genders in the singular:

• un cotxe gran = a big car
• una casa gran = a big house

So even though casa is feminine, gran stays gran.

You can tell because it takes the feminine article la:

• la casa

Many Catalan nouns ending in -a are feminine, and casa is one of them. A good habit is to learn nouns together with their article:

• la casa
• el llibre
• la taula

That makes gender much easier to remember.

Casa is pronounced roughly like KAH-zuh in Central Catalan, though the exact final vowel sound can vary by dialect.

A simple learner-friendly breakdown:

• ca- sounds like kah
• -sa sounds like a soft zuh or suh, depending on dialect

The c here is a hard k sound, because it comes before a.

A simple approximation for English speakers is:

lah KAH-zuh ez grahn

A few notes:

• la = lah
• casa = KAH-zuh
• és = ez
• gran = grahn

The r in gran is not like a strong English r. It is lighter, often tapped.

Yes, Catalan often leaves out subject pronouns, but not the noun itself when you need it.

So you can say:

• És gran = It is big / He/She is big, depending on context
• La casa és gran = The house is big

In your sentence, la casa is included because you want to say exactly what is big.

Yes, often you can. Grossa can also mean big.

Very roughly:

• gran = big / large, often neutral and very common
• grossa = big, large, sometimes with a sense of physical bulk or size

For a house, both may be possible depending on context, but gran is a very natural basic choice for learners.

It is neutral and works in both formal and informal situations.

La casa és gran is just a basic descriptive sentence, so you can use it in normal speech, writing, or language exercises without any problem.