Using this circuit you can convert the 12V dc into the 220V Ac. In this circuit 4047 is used to generate the square wave of 50hz and amplify the current and then amplify the voltage by using the step transformer.
How to calculate the transformer rating
The basic formula is P=VI and between input output of the transformer we have Power input = Power output
For example, if we want a 220W output at 220V then we need 1A at the output. Then at the input, we must have at least 18.3V at 12V because of 12V*18.3 = 220v*1
So you have to wind the step up transformer 12v to 220v but input winding must be capable to bear 20A.