How much juice is in a pineapple
I do believe your answer can be found in this totally over the top experimental comparison of two juicers. There's loads of info there, but I think the relevant part is when the author discusses the actual yields for each juicer. For pineapple, the author finds the yield to be between 71% - 76% of the total mass of the pineapple. So give it a weigh, and you should get about 3/4 that much juice. I assume the experiment skinned and cored the pineapple, so you'll need to account for that. 

I'm assuming you're using a juicer to get your juice. Note that the juicers used in the above experiment were $400 and $500 respectively, so I assume they are pretty high end. You mileage may vary with a lower quality product. 

And since you didn't ask for weight, I just tested weight to volume, 6 fluid oz of pineapple juice weighs 6.5 oz (so it's a bit denser than water). So one pound of pineapple should yield about 11 oz or just under a cup and a half.