Debating whether to go 1×9 or 1×10 from my current double ring set up with a road block at the rear. Currently have a 22t granny with 11 – 25t cassette, would probably go to 32t front and 11 – 36t rear if I changed, how do I calculate whether the highest/lowest gears are comparable?

Teeth on front/teeth on back X circumference of wheel.

so

22/25 = 0.88

or

32/36 = 0.88

Ignoring the wheel size. Therefore no change in gears?

Sounds right. If you’re not changing wheel/tyre size, you can ignore wheel size completely and just use the ratio.