How much juice is in 1 pear
Study linked below states that pears are made up of 84% water. So 84% of the weight of the pear in grams would be a close estimate to the weight of water of the pear, in grams. Water weighs 1 ml per gram, so you could then convert the weight in grams of the water to ml of water in the pear.

Water Content of Fruits and Vegetables