What is the net worth required to retire in Singapore if you are small family with yearly expenses of 50k sgd

Since no liability. Tbh you can retire comfortably already. And assuming your child is grown up of course. With insurance sufficiently covered

How old are your children and do you plan to send them for overseas university education or local uni?

That may be the largest single expenditure to consider. Once that is factored for, then the others are regular expenses.

I will do the below:

1. 1 mil to buy a house.
2. 1.5 mil to invest and get at least 4 % dividend.
3. 1 mil as spare cash.

You need to decide if rental yields Are gonna increase vs your investment returns. Look at the projected rise in your biggest expenses which prob will be rent.