The way to work out what you need in retirement is to do a budget planner that is relevant for today and then cross off all of the things that will stop in retirement.
For example if you spend £2000 a month now including everything and these were the outgoings that will stop in retirement
Mortgage - £300
Life assurance - £20
Car loan - £150 (assuming you buy a car in retirement rather than lease)
Pension contributions - £130
Travel to work - £50
Lunches - £50
Then you will need £1300 in retirement.
Let’s say you want to join a gym though and do a couple of other things and these will cost £100
You will need £1400.
Find out what your state pension is - easily done. Let’s say in this case it is £750 a month.
You will then need £650 a month from elsewhere.
Realistically, to get this and to ensure it lasts in retirement you will need a pot of around £150,000.
However if you are in a couple then you will get two state pensions so you may have enough albeit one will die at some point so having some money saved for this eventuality is still adviseable.
Defined benefit is different of course. With this you know what you are going to get or thereabouts as you get a statement every year telling you.
If you have built up say £5000 a year then that is the equivalent of having a pot worth over £150k because it would cost you that to buy an income for life of £150k
That’s why defined benefit schemes are so valuable.
If you want to retire before state pension age then you will need more.
The vast majority of people in the Uk do not have anywhere near enough in their pension schemes.
This is very simplistic but it may help.