LARGE VS. BIG

'Large' and 'big' are both regular adjectives...

COMPARATIVE FORMS!
Their comparative forms are 'larger' and 'bigger',
Their superlative forms are 'largest' and 'biggest'.

'Big' is a very common word in both written and spoken English; in fact, it's in the top 1,000 most frequently used words.

'Large' , on the other hand, is a less frequently used word and doesn't even make it into the top 3,000 most frequently used words in English.

Now, onto the question of meaning ...

The general meaning of both 'large' and 'big' is:
'of more than average size/amount/weight/height' etc.

For example:

'Mohan has got a well-paid job and can afford to live in a house'

OR

'Mohan lives in a large house'.

In these examples, both 'big' and 'large' mean that Mohan's house is of more than average size.

Although 'big' and 'large' both mean the same in these examples, 'large' sounds a little more formal.

##IMPORTANT
Neither 'large' nor 'big' can be used with uncountable nouns.

This means, we can say:

'The house has a ( big or large ) garden' - because 'garden' is countable .
However, we can't use 'big' or 'large' with 'traffic', because 'traffic' is uncountable.

With uncountable nouns, you can use 'a lot of' - for example:

'There's a lot of traffic on the road next to the house.'

So, although 'large' and 'big' are often interchangeable, sometimes they are not.
So next, I'll try and give you some examples of when this is the case...

'Big' can mean 'important', for example:

'Buying a house is a very big decision'.

It can also be used in informal situations to mean 'older', for example:

'He's my big brother' ...

as well as  'successful' or 'powerful', for example:

'York is a big tourist destination'.

Also in informal situations , we can use 'big' to mean 'doing something to a large degree', for example:

'She earns a lot of money, but she's also a big spender'

OR

'I'm a big fan of yours'.

'Big' is used in a lot of fixed phrases , and because these phrases are fixed, to change 'big 'to 'large' would sound wrong. Examples of fixed phrases using 'big' include:

'It's no big deal' - it's not really important.

'I have big ideas for this house' - impressive plans for the future.

'She's a big mouth' - a person who can't be trusted to keep a secret.

'He's too big for his boots' - too proud of himself.

There are also some fixed phrases using 'large' .

Examples include:

'The prisoners are at large' - they have escaped and may cause harm.

'She's larger than life' - more exciting or amusing than most people.

Finally, quantity words ....
'large' , more often than 'big', is used with the following quantity words:
'a large amount', 'on a large scale', 'a large number of', 'a large quantity of', 'a large proportion', 'to a large extent', 'a large percentage of', 'a large part of', 'a large volume' and 'a large area'.

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