Sushi is traditionally made with rice, seaweed and seafood. Because most types of seafood are relatively low in calories, most kinds of sushi are as well. However, calories in sushi vary depending on the dish, the portion and how it's prepared. In fact, the same sushi dish may have a different nutritional profile when it's prepared by a different chef, depending on the specific mix of ingredients.
If you're watching your calories, sashimi (raw fish) and nigiri (raw fish on a small bed of rice) are good options. So are sushi rolls made with fresh or pickled vegetables. You can also ask for sushi made with a smaller portion of rice. Anything with mayonnaise or added sauce and anything that's fried will have higher calorie counts.