The short answer is 1.00 in the better eye. The long answer is that there is
no short answer.

"Satisfactory" varies by person and by situation. People tolerate
cylindrical blur differently.

If you're nearsighted, you're familiar with the blur that your astigmatism
causes. When you take off your glasses, how well do you see up close? It
takes a lot of astigmatism to reduce vision to disabling levels.

Many times astigmatism is better in one eye, and it becomes the "dominant"
eye so that spherical (non-toric) lenses in _both_ eyes gives "satisfactory"
vision.

Sometimes ordinary soft lenses correct your astigmatism partially, and the
approximation is fine under goggles, water sports, etc. where elsewhere you
could use glasses.

Glasses can be designed to add astigmatism correction over ordinary
spherical contacts, for driving at night or reading the cable guide.

-MT

Usually at least -.75 to -1.25 for torics. If you have less than -.75
you get regular lens and perhaps a -.25 bump in spherical eqivalent. Up
to -1 cylindar can be corrected fine with soft lens, use -.5 spherical
equivalent.