Regarding transformers there's physical construction calculations.
And there's electrical calculations. They go hand in hand.
Both have a myriad of parameters to wade through.
Above is a page from an article in 'The Boy Mechanic' (published by Popular Mechanics around 1950),
telling dimensions for various transformer types. The internet has more modern resources to find specs and formulas.
I recommend a very good book which I have in my personal library as below,
Practical Transformer Design Handbook by Eric Lowdon
For your info that this book includes a number of easy to use spreadsheets in printed form