Once you’ve selected “tile all pages,” it will give you
the option to input a scale factor.
I personally don’t think this is as handy as imputing a
size, but with a little math you should be able to scale
it up or down as needed.
Unless you’re Craft Bunny, who hates math, and then you
just play with numbers until it prints out something
that looks like a size you could stitch.
I wouldn’t recommend the Craft Bunny way, but in a
pinch, it works.