Joshua Katz, a Ph.D student of statistics at North Carolina State University, just published a group of awesome visualizations of Professor Bert Vaux and Scott Golder's linguistic survey, which looked at how Americans pronounce words (via detsl on /r/Linguistics).
Nutritional Facts. 1 cup jambalaya with 1/2 cup rice equals 302 calories, 6 g fat (1 g saturated fat), 125 mg cholesterol, 450 mg sodium, 34 g carbohydrate, 5 g fiber, 27 g protein. Diabetic Exchanges: 3 lean meat, 2 vegetable, 1 starch.
If you measure and use exactly the stated as a serving for that product, you will find approximately how many calories you are getting from it. If you use double the amount, then double the amount of calories. A good educated guess would be approximately 150 Calories on average bread with an average jam or jelly. **If you are wanting to know how many calories are in specific homemade products, you would need a calorimeter. Most products in America these days list the nutritional data on their labels.