In direct answer to your question, you can almost certainly find the formula on the front of the LFPF homepage or with a second of googling.

You'll find that most lenses have huge aberrations when focused that close. Getting to 1x with good quality requires a macro lens and even then it's going to start looking bad probably by 4x. At 10x, you're going to have mush from any lens not designed for use at that range, i.e. microscope objective lenses. If you're using normal lenses for very high magnification, you can somewhat avoid this problem by using the lenses reversed because they are generally well-corrected for the rear image plane being very close and the front image plane being further away. If you want a 10x shot, set it up like a 0.1x shot but swap the film and subject locations.

Don't forget also that diffraction gets worse: a 2x bellows extension to reach 1x magnification will double the effective focal length and add two stops to your effective aperture. Go to 5x or 10x and you'll find that diffraction means you need to be shooting at much larger apertures than you're used to so the DOF will be practically nil.

If you want to do ultra-macro and despite this being APUG, I strongly suggest looking into the newer digital techniques like focus-stacking. It also helps that there are lenses available for 35mm that are specifically designed to reach about 6x magnification. Right tool(s) for the job and all that.