Which count Aida for this cushion please?

[mineymo]

I'm attempting to design a cushion cover but struggling to know what size Aida to use. Help please!?

Ultimately, I'm trying to end up with a 30*30cm cushion that has a moon with a diameter of approx 30 stitches in the middle with approx 15 stitches either side and top and bottom.

An example that has the same size stitches that I am aiming for appears to have ~70 stitches for 35cm (14 inches) so therefore 70/14=5 stitches per inch. Would I use 5 (possibly 6 since 5 doesn't seem to exist) count Aida to achieve the same effect? That doesn't sound right as cushion kits seem to come with 10 count aida (based on a quick peruse of John Lewis). Kids kits come with 6 count aida!

Would I use tapestry wool or something bigger?

Thanks :-)