One Less Or One Fewer [People Say Different Things]?

Informally, people use them both. The countable and non-countable categories are just a broad general rule (to which there are exceptions). Fewer is normally used when it is followed by a plural count-noun. For example:

I have fewer things on my list to do.

So, for most of your examples, I would go with "one less."

There, I'm done. That's one fewer/less thing I need to do.
There, I'm done. That's one thing fewer/less I need to do.

That is 2 fewer/less things I need to do.

That's one fewer/less gift I have to buy you since you didn't get an A.

It took a few less bullets to kill him.
I would re-write this to make it less confusing. "It didn't take as many bullets to kill him."

I have one point less/fewer in every category.
I have one less/fewer point in every category.

There is one less/fewer player on the team this season.

There is one player fewer/less on the team this season.

This recipe uses two less(er) apples than...

(Others may disagree with this.)

Since its 2 things or apples, shouldn't it be fewer?

That is 2 fewer/less things I need to do.

This recipe uses two less/fewer apples than...

Thank you

AnonymousWhich are correct please?

Technically, 'fewer' goes with countable nouns thus:

That's one fewer thing I need to do.
That's one thing fewer I need to do.
That is two fewer things I need to do.
That's one fewer gift I have to buy.
It took a few fewer bullets to kill him.
I have one point fewer in every category.
I have one fewer point in every category.
There is one fewer player on the team this season.
There is one player fewer on the team this season.
This recipe uses two fewer apples than...

Nevertheless, it is quite common to substitute 'less' for 'fewer', and not many people would object if you made that substitution in all the sentences above. In fact, some would recommend it, especially in awkwardly repetitious constructions like 'a few fewer', which sounds so odd that it is almost always said as 'a few less'.

CJ

Would you substitute less for fewer in the following yourself? Because although the nouns are countable we are talking about one and not 2 things or gifts?

That's one fewer thing I need to do.
That's one thing fewer I need to do.

That's one fewer gift I have to buy.

Here I would leave fewer as there are 2 things.

That is two fewer things I need to do.

Thank you

AnonymousWould you substitute less for fewer in the following yourself?

Yes, in every case. But then I don't always speak the way the grammar books tell me to.

CJ

Good to know that you would use 'less'

Would you tell me if this is correct?

For every 30 ml of water, you need to put one dose of formula. At night I put in one less doses. I put in 2 dose for 90ml instead of 3 doses.

Is this grammatical?

Thanks

AnonymousFor every 30 ml of water, you need to put one dose of formula.

"Dose"? "dose" is used for medications, i.e., drugs. I think you need a different word, but I don't know anything about baby formula, which I assume you mean, so I don't know the word for that. Something like spoonful or packet would be better.

Let's assume for now that "dose" is OK.

AnonymousAt night I put in one less doses. dose.

You can't have one doses. 'less' instead of 'fewer' is not a serious mistake.

AnonymousI put in 2 two dose doses for 90ml instead of 3 three doses.

You can't have two dose. I think you're just not paying attention. You know this.

The usual practice is to spell out one-digit numbers.

CJ

Didn't you say it was 'one less dose' or 2 fewer doses?

Thanks