[1] https://medium.com/@tabitha.whiting/should-you-swap-plastic-... "The study estimated that a cotton tote bag’s total carbon footprint was 598.6lb of CO2e. This compared to 3.48lb of CO2e for a standard plastic bag. That means that you would need to use the tote bag 172 times for every 1 time you used the plastic bag."
The reason these laws get enacted is because not enough of the plastic bags end up in landfills.
[1] https://www.scientificamerican.com/article/from-fish-to-huma...
There are so many factors involved (CO2, petroleum drilling, microplastics, other pollution, etc) that it's not easy to provide a definitive ratio. I do think it's good that the discussion has reduced the amount of plastic being used in the bags themselves (though I'd need to see a study if that ends up reducing the total amount of plastic involved, or if they're just using more bags). I think it's good that people are now in a better position to forego bags entirely rather than put a single item in a bag simply because they're there and free.
Mostly, though, I'd caution against citing numbers that assume that one reusable bag is exactly the capacity of one disposable one.