I'm thinking about a few more lbs in secondary but for the moat part I'm worried about sg, I guess I will be flying blind I don't have a refractometer to measure the sugar in the pears is there another method?
I'm paranoid as it's the first attempt but no matter what it will turn out good I'm sure if not I'll age it some more.
Perry is made from straight pear juice. Watering it down will make a weak tasting low ABV beverage that won't age all that well. Grind the pears, let sit out overnight, juice the next day, ferment the juice. You will love the results.
If I understand the question, you r asking if 20lbs of pears will make 5 gal. I believe I read that it takes 12 lbs of apples to make a gallon. So it may be more. You posted you may end up with 40lbs. That will be a lot closer.
I cant remember what they call it, but some people use to make a second batch of cider by taking the previously pressed apples soaking in water over night and then re-pressing. Obviously not as strong as the first press but would still have a pear flavor. Perhaps good enough to top off your carboy if you were close to 5 gal.