If I have a prescription for
sphere-175, cylinder -.50 and axis 125
and my next presciption is for
sphere -325, cylinder -100 and axis 170

how far can I see right before I get the new prescription filled?
what do these numbers actually mean?

It's difficult to correlate the prescription with your visual acuity. A good estimate is one line for every 0.50 spherical equivalent. If you're 20/20 with your new correction, then with the old correction, you may see around 20/40 or 20/50? This is only a guess.

The sphere is correction for myopia (near-sighted) or hyperopia (far-sighted). You're a myope with some progression. You've changed from a -2.25 to a -4.25. The cylinder is correction for astigmatism. You have 1.00 cylinder of astigmatism.

thank you that helps a lot