Look on the nomenclature tag on the fan motor. It gives the mfd capacity rating for the motor. A 35/5 cap means the the compressor requires a 35 mfd cap and the fan uses a 5 mfd cap. Installing the wrong capacitor will cause motor failure. It will overheat and melt the windings in about a day if wrong so it is important to not guess. Usually (but not always) a standard quarter horse motor with 1050 speed takes a five mike capacitor. A third horse motor requires a 7.5 microfarad cap. A half horse motor usually takes a 10 MFD cap. I sold Magnetek, AO Smith, and Packard motors when I was in the biz. If you are unsure about matching a motor you do not always go by horse power rating. You go by amp draw. Horse power rating can be faulty but amp draw rating tell no lies.
The primary speed on these condenser motors is usually 1050 rpm but more expensive better built motors speed @ 825 require more exotic capacitors with lower ratings. These motors have special fan blades engineered to move air in a specific way. These motors last longer and are way more expensive and if you plan on using a 1050 motor as a replacement you would be screwing up big time. So it is vitally important to get it right. My 2 cents.