Under Export UV Layout in the uv image editor you can set the dimensions of the layout in the bottom left corner.
I think you can even export it as svg.
when you open up uv editor, bottom centre new image, determines image size before unwrap. unwrap. export uv as png. job done
Imagine if i set it 3x bigger, wont it affect the way uv’s are wrapped around the mesh?
Indeed, that’s what i do