Please forgive the question – I aussume this has been asked many times, but I couldn’t find an answer which was simple enough for me to understand.

If I want to go 1×0, but want a climbing gear which is the euqivalent of my current 22/34 combination, what 1×10 combination do I need?

Assuming a 34t cassette with your 22 granny you’d need about 28 up front with a 42t expanded cassette. But unless you need to spin up walls a 32t should be plenty, I run 36t

30/42 will probably be the closest practically speaking.

For XX1 but easy enough read off what you want but probably a direct mount 26t.

Or go higher and work on it (currently on 32-40 and 32-42 in hilly terrain

Even 28/42 isn’t quite as low as 22/34, if you truly need a gear that low then single ring may not be for you, and sticking with a double makes sense!

Do a search for Sheldon Brown gear calculator and plug in the specifics for your bike.

Assuming:

Same crank length before/after conversion
Same wheel size before/after

then:

22/34 = 0.65 (decimal)

so if you want 30T front ring, you’ll need a 30/0.65 = 45T rear.

In straightforward terms, currently your rear cog has almost 50% more teeth than the front one, so this is the situation you have to preserve (with the same cranks/wheels) if you are to get an equivalent gearing on a different setup.

Seems like the recipe for selecting your rear cog maximum will be to find out what the smallest front ring you can accommodate is, then add 50% to that number of teeth and see if such expander rings are available in that size. I doubt you’ll get an ‘off the shelf’ cassette to suit unless you can fit a very small front ring. Other variables like crank length could be altered (lengthened) if you are comfortable.

Do you know what the smallest ring size you can accommodate up fron on your 1×10 would be?