The answers depend in part on what you expect from an energy bar and on the bar you choose. The original energy bars were chewy, high carbohydrate bars that tasted bland and with added vitamins and minerals that left a metallic aftertaste. Today, many taste more like candy than nutritional bars.
Energy bars vary from just over an ounce to nearly four ounces.
In general, the larger the bar, the more calories it contains. Today's bars are not always. Of five bars recently picked up at random from my local supermarket, the percent of total calories from fat varied from 8 to 40, with as much as 60 percent of the fat coming from saturated fat. Look for a bar with less than 30 percent of total calories from fat and no more than 5 grams of fat per bar. If you're watching calories, choose bars with less than 200 calories.