Ого, какой большой дом!

Ого is an interjection, like Wow!, Whoa!, or Gee! in English.

In this sentence, it adds surprise or admiration before the rest of the exclamation:

• Ого, какой большой дом! = Wow, what a big house!

A few useful notes:

• It is common in spoken Russian.
• It is a bit informal, but very natural.
• You can also say the rest of the sentence without it: Какой большой дом!

Because какой is used in exclamations before a noun, especially in patterns like:

• Какой + adjective + noun!

So:

• Какой большой дом! = What a big house!

Here какой means something like what a / what an / how ... a ...

By contrast, как is usually used with:

• verbs: Как ты живёшь? = How do you live?
• adverbs or adjectives without this noun pattern: Как красиво! = How beautiful!

So:

• Какой большой дом! = correct
• Как большой дом! = not correct in this meaning

Because какой has to agree with дом.

The noun дом is:

• masculine
• singular
• nominative

So какой also appears in the masculine singular nominative form:

• masculine singular nominative: какой
• feminine singular nominative: какая
• neuter singular nominative: какое
• plural nominative: какие

Compare:

• Какой большой дом! = What a big house!
• Какая большая комната! = What a big room!
• Какое большое окно! = What a big window!
• Какие большие дома! = What big houses!

For the same reason: adjectives must agree with the noun they describe.

Since дом is masculine singular nominative, большой is also masculine singular nominative.

Compare:

• большой дом = big house
• большая комната = big room
• большое окно = big window
• большие дома = big houses

So in какой большой дом!, both какой and большой match дом.

Because this is an exclamation naming or presenting the thing being reacted to, and Russian normally uses the nominative for that.

Even though there is no verb here, the noun stays in its basic dictionary form:

• дом

This is very common in Russian exclamations:

• Какой красивый город!
• Какая хорошая погода!
• Какое интересное имя!

So the structure is basically:

• What a/an + adjective + noun! and the noun appears in nominative.

Russian often leaves out a verb in short exclamations like this.

English says:

• What a big house!

Russian does the same kind of thing:

• Какой большой дом!

There is no need to add a verb such as is. In fact, adding one would usually sound unnatural here.

This is just a normal exclamatory pattern in Russian.

Because Russian does not have articles.

English distinguishes:

• a house
• the house

Russian just says:

• дом

The exact meaning depends on context.

So Какой большой дом! can correspond to:

• What a big house!
• sometimes, depending on context, something like What a big the-house-we’re-looking-at is!

But in this exclamatory sentence, English naturally uses what a.

Yes.

• Ого, какой большой дом! = Wow, what a big house!
• Какой большой дом! = What a big house!

Adding Ого makes the reaction stronger and more conversational. Without it, the sentence is still completely natural.

Yes, but Какой большой дом! is the most straightforward and common order.

Russian word order is flexible, and changes in order often change the emphasis.

For example:

• Ого, какой большой дом! = neutral, natural exclamation
• Ого, дом какой большой! = more conversational, with extra focus on how big
• Какой дом большой! = possible, but usually less natural in this exact situation than Какой большой дом!

For learners, the safest pattern is:

• Какой/Какая/Какое/Какие + adjective + noun!

The sentence is natural in everyday speech, and Ого makes it feel informal and spoken.

• Ого is conversational.
• Какой большой дом! itself is neutral and can be used in many situations.

So:

• with Ого → more casual, expressive
• without Ого → still expressive, but less colloquial

It would usually have strong exclamatory intonation.

A speaker typically:

• says Ого with surprise
• stresses большой or дом depending on what feels most impressive
• drops the voice at the end like a complete exclamation

The comma after Ого reflects a small pause:

• Ого, какой большой дом!

So in speech, it feels like:

• Wow — what a big house!