A typical parlor pizza is 14 inches in diameter. From geometry that is 154 square inches (or 154 pieces of pizza that 1inch by 1 inch). A 14 inch pizza has a total of 2280 calories on average. If cut in 8 slices, that is 285 calories per slice on average. Doing the math, you can estimate that for every square inch (1inch long by 1 inch wide) you are eating 15 calories. (11 calories for thin crust, 19 cals for thick or Sicilian crust). Using 15 calories for one square inch helps since pizza slices come in sizes (jumbo, large, small slices). Take a peak at a ruler, and use your thumb or finger width to estimate this length. Since a slice is a triangle...just do your best (unless you are a geometry nerd 1/2 base x height. Uggh). 15 calories per 1 inch square.