Sushi - estimating calorie content, healthiness

1. Given that sushi preparation varies so much from restaurant to restaurant (e.g. I've had massive maki (rolls) and tiny ones . . . even variation in how much avocado, etc is in each roll), is it even possible to effectively estimate/log calories in sushi if you're not eating at a chain restaurant?

2. I always thought of sushi as a healthier option (as long as you pick the sushi that are more about fresh ingredients and not full of mayonnaise, shrimp tempura etc), but is this really true? I always figured sushi aren't fried (again, unless you get maki that are full of fried stuff etc), come in a way smaller serving than most restaurant meals, and are mostly just like fresh fish, tiny amounts of rice, and seaweed.

Are they a lower calorie option compared to the standard burger and fries? Because the database seems to have no idea and now I'm doubting myself.