As a Registered Dietitian, it is some times difficult to explain to people exactly what they are eating. I am a fan of visual models, having used tubes of fat, a 51b fat model and containers to show what exactly is a whole grain.
The Sugar Stacks site is helpful to see exactly how many sugar grams are in foods and beverages. There are 4 calories per gram of carbohydrate, so you can see how quickly the calories add up. There are 4 grams per cube (so 16 kilocalories per cube).
At the site you can check out the sugar in cookies, sauces, desserts, snacks, smoothies and more.