Compare foods by calorie density.
Energy density is calories divided by weight, and it predicts how much food you get for a given calorie budget. Foods under about 1.5 kcal/g — most vegetables, fruit, broth soups and lean protein with water in it — let you eat a satisfying volume for few calories. Above roughly 4 kcal/g, portions shrink fast. Comparing two foods on the same per-gram basis strips out serving-size differences.
Energy density comparison
Density = calories / grams; ratio = density A / density B
These figures are population-average estimates for general planning only and are not medical or dietetic advice. Individual energy and nutrient needs vary widely with body composition, activity, medication and health status. Consult a qualified health professional or registered dietitian before making significant changes to what you eat, and especially if you are pregnant or breastfeeding, are under 18, or have a medical condition or a history of disordered eating.
Below about 0.6 kcal/g is very low (most non-starchy vegetables, broths), 0.6-1.5 kcal/g is low (fruit, cooked grains, lean protein), 1.5-4 kcal/g is medium (bread, cheese, dried fruit) and above 4 kcal/g is high (oils, nuts, crisps, chocolate).
Not on its own — it means fewer calories per gram. A very large portion of a low density food can still add up, but research on satiety consistently shows people eat a fairly constant weight of food, so lower density usually means fewer calories eaten.
Use the weight as you eat it, and use it consistently for both foods. Cooking changes water content and therefore density, so raw pasta at about 3.7 kcal/g becomes roughly 1.3 kcal/g once boiled.