How much do they add to your shoe size?

there are some factors to consider.
thickness of neoprene, how tight they are on your foot to start & if your going to be wearing socks. If so, how many? what brand are you asking about?

I went one size up and they are snug when I wear my thick wool socks. I should have gone 2 sizes.

I have cheap breathable waders from Bass Pro and the cheap canvas lace ups from Academy.

If you go to academy, just open a box and throw a leg in there and see how it fits. No use in buying something thy doesn't fit.

I wear a 9.5 shoe and went with size 11 wade boots.
That works great even in the winter when I wear heavier socks.
Buy waders that are close to your normal shoe size. The neoprene feet stretch.

I prefer stocking foot waders with the pedal drive. Boots need to be 2 sizes up with the heavy socks.

1 1/2 is about right