Let's take your one tire size example, 265/70R17
The first number is the tire width in milimeters
The second number is the percentage of that width that makes the sidewall height
The third number is wheel diameter in inches
(Yep, we have mixed units for our tires!)
So if you have a 245/70R17 tire and a 265/70R17 tire, the second tire is going to be both wider AND taller because 70% of 265 is more than 70% of 245.
A 245/70R17 and a 265/65R17 are roughly the same height, for example.
Something else to remember is the sidewall height is just from edge of wheel to the tread. Total tire height is twice that number, plus the wheel size.
Instead of trying to do all the math manually (especially with mixed units), this website is very handy for running comparisons:
https://tiresize.com/calculator/
Just wait until you get into wheel sizes with width, backspacing, offset, etc - yep they have mixed units too