èr bǐ yī dà.

比 is the word used to make a comparison. In this sentence, it means than.

So:

• 二比一大 = Two is bigger than one
• literally: Two, compared with one, is big

A very common pattern is:

A 比 B + adjective

which means:

A is more adjective than B

Examples:

• 他比我高。 = He is taller than me.
• 今天比昨天冷。 = Today is colder than yesterday.

Chinese follows a very regular comparison pattern:

A 比 B + adjective

So in 二比一大:

• 二 = the thing being described
• 比 = than / compared with
• 一 = the thing it is compared to
• 大 = big

So the structure is:

• A: 二
• 比 B: 比一
• adjective: 大

English says A is bigger than B, but Chinese says something closer to A compared with B big.

In Chinese, adjectives can often function like verbs, especially in simple descriptions.

So 大 does not just mean big; in a sentence it can mean is big.

That is why:

• 二比一大。 naturally means Two is bigger than one.

You do not say:

• 二比一是大。 ❌

In this kind of sentence, 是 is not used before the adjective.

By itself, 大 means big. But in the pattern A 比 B + adjective, the comparison makes it mean more adjective, so here 大 is understood as bigger.

So:

• 大 = big
• 比...大 = bigger than ...

Similarly:

• 高 = tall
• 比...高 = taller than ...
• 快 = fast
• 比...快 = faster than ...

Yes. 一比二小 means One is smaller than two.

Both sentences are correct:

• 二比一大。 = Two is bigger than one.
• 一比二小。 = One is smaller than two.

Chinese often lets you choose the direction of the comparison depending on which adjective you want:

• 大 = big
• 小 = small

In this sentence:

• 二 is pronounced èr with a falling fourth tone
• 一 is written yī, but in actual speech its tone often changes depending on what follows

Since 一 comes before 大 (which is fourth tone: dà), 一 is usually pronounced yí here.

So the sentence is commonly pronounced:

èr bǐ yí dà

This is because 一 changes tone in normal speech:

• before a fourth-tone syllable, 一 is usually pronounced yí
• before other tones, it often becomes yì

Learners should know that the dictionary form is yī, but tone change is very common in real speech.

Chinese comparisons are often made with 比, not with a separate word meaning more before the adjective.

English:

• Two is bigger than one

Chinese:

• 二比一大

You do not normally say:

• 二比一更大 in a basic comparison unless you specifically want extra emphasis like even bigger or still bigger

So for a simple comparison, 比 + adjective is enough.

No, that would not sound right in a normal comparison sentence.

After 比, the adjective usually appears directly:

• 二比一大。 ✅

Not:

• 二比一很大。 ❌

That is because 很 is often used in plain descriptive sentences, such as:

• 这个很大。 = This is very big / This is big.

But in a 比 comparison, you normally just use the adjective itself.

You can add a degree word after the adjective, often with 了 or words like 多了.

For example:

• 二比一大多了。 = Two is much bigger than one.
• 他比我高多了。 = He is much taller than me.

So the basic form is:

• A 比 B + adjective

And a stronger form can be:

• A 比 B + adjective + 多了

It is understandable and grammatically correct, but it feels like a very basic teaching example because it compares numbers as if they were physical sizes.

In real life, when talking about numbers, Chinese speakers are more likely to say:

• 二比一大。 = Two is greater than one.
• or more explicitly:
• 二比一大得多。
• 二大于一。 = Two is greater than one.
  This is more mathematical or formal.

So 二比一大 is fine for learning the grammar pattern A 比 B + adjective, even though the context is very simple.

Here you should use 二, not 两.

That is because 二 is the basic number two, especially when counting, doing math, or talking about numbers themselves.

Examples:

• 一、二、三
• 二比一大。
• 二加二等于四。

两 is usually used before measure words and nouns:

• 两个人 = two people
• 两本书 = two books

So in this sentence, because you are comparing the numbers themselves, 二 is correct.