3.2 - 4.00 pH (approximate)
Because Pineapple has an approximate pH of 3.6, Pineapple is considered very acidic and you should think twice before eating Pineapple with gastritis or reflux. If you must eat Pineapple, try eating just a little one day and see how you do before eating more. Come back and let us know how you did in the comments below.
Remember, everyone is different and there might be reasons besides pH that make this food intolerable, triggering of reflux, or beneficial. Check out comments below to see what other people's experiences have been with eating Pineapple and please consider sharing your own knowledge to help others.