How do I save a custom shape as a tool preset whilst keeping to a desired height and width?

on the path options drop down menu the option to change to a fixed size isn't there?

@28989718 

I just tested on macOS and get the same results that you do. It appears to work as long as I stay in the same document. The stroke, width, and height are all there every time I click to create the shape.

When I start a new document, the 5px stroke is there, but not the width nor the height (as you saw).

However...

When I reset the toolbar in the first document and the W & H return to zero, then choose the preset again, the preset does not pick up the W&H. They are not actually part of the preset, they are simply remaining in your options bar. This is why it's not working as you hoped it would.

You can put in a feature request for the shapes to include the size (as the Crop tool does) by starting a new post and tagging it as an idea. I hope this answers your question

Jane