Sugar ratios

Alright, so i juiced a sample of the apples I collected, took a reading, and ended up with an OG of 1.055. I'm fermenting 15 gallons. If it ferments dry to .995, that would give me an ABV of 7.8%. I'm planning on adding another 5 gallons of unfermented juice and a few cans of concentrate plus sugar for back-sweetening and adding more apple flavor to the cider for a total of 20 gallons which would make an ABV of 5.8%. My goal is to get above 6%, so more like 6.3-6.5% after dilution. I already figured that this would mean I need an OG of 1.06. My question is, how much sugar would I have to add to a 15 gallon batch to increase the gravity .005? Is there a formula to see how much sucrose to water is needed to increase the gravity by .01?

Five points is 2.25 oz/gal

5 points as in 1.055 to 1.06? So just over 2 pounds for 15 gallons then for my goal? Thanks, just trying to be completely clear.

yep