The scores
Hill's Science Diet Indoor Cat: C (60/100)
Royal Canin Indoor Cat: D (45/100)
A 15-point gap that crosses a full letter grade. Hill's lands in the lower-middle of C territory — not great, but acceptable. Royal Canin falls into D territory, which means its ingredient quality is below the standard we'd consider adequate for most cats. For two brands that command premium prices and carry vet endorsements, these scores may surprise some owners.
How the ingredients compare
Here are the first five ingredients side by side:
Hill's Science Diet: Chicken, Whole Grain Wheat, Corn Gluten Meal, Chicken Meal, Powdered Cellulose
Royal Canin: Chicken By-Product Meal, Brewers Rice, Corn, Wheat Gluten, Corn Gluten Meal
Hill's starts with chicken — a whole, named meat. Royal Canin starts with chicken by-product meal, which is rendered leftover parts (feet, necks, intestines) rather than the meat itself. Hill's second ingredient (whole grain wheat) isn't ideal for a cat, but at least it's a whole grain. Royal Canin's second ingredient (brewers rice) is a processed grain fragment left over from milling. The pattern continues: Hill's ingredient list is a step above Royal Canin's at virtually every position.
Where Hill's Science Diet pulls ahead
Chicken first. The single biggest difference. Hill's leads with chicken — a whole meat that contains quality animal protein, fat, and moisture. Royal Canin leads with chicken by-product meal, which is a dry, rendered product made from parts of the chicken that aren't considered meat. For an obligate carnivore like a cat, having a whole animal protein as the primary ingredient matters.
Chicken meal at position four. Hill's includes chicken meal (a concentrated animal protein) as its fourth ingredient, adding another named animal protein source higher in the formula. Royal Canin's fourth ingredient is wheat gluten — a plant protein that inflates the protein number without providing the amino acid profile cats need.
Fewer grain fillers in top five. Both brands use grain fillers, but Royal Canin uses more of them: brewers rice, corn, wheat gluten, and corn gluten meal all appear in the first five. That's four grain-based fillers out of five ingredient slots. Hill's has two (whole grain wheat and corn gluten meal), which is still not ideal but noticeably better.
Lower price. Hill's Science Diet typically costs less than Royal Canin per pound. Getting better ingredients for less money makes the choice even more straightforward. Shop on Amazon →
Where Royal Canin holds its own
Breed-specific and condition-specific formulas. Royal Canin offers an unusually wide range of specialized formulas — breed-specific, weight management, urinary health, digestive care, and more. If your vet has recommended a very specific Royal Canin therapeutic formula for a diagnosed condition, that recommendation may override general ingredient quality comparisons.
Feeding trial research. Royal Canin invests significantly in feeding trials and has decades of nutritional research behind their formulas. Their approach is more clinical than ingredient-focused, and some veterinary nutritionists value this methodology highly.
Palatability. Royal Canin consistently ranks high in taste-test studies. Their kibble shape and coating are specifically engineered for palatability. If you have a picky cat that refuses other foods, Royal Canin may be one of the few brands they'll eat. Shop on Amazon →
The bottom line
Hill's Science Diet is the better choice between these two, scoring 15 points higher with a meaningfully stronger ingredient list. Chicken first versus chicken by-product meal first is a clear and significant difference. Both brands lean heavily on vet recommendations and clinic partnerships for their reputation, but when you compare what's actually in the bag, Hill's delivers more for less money. That said, neither brand is truly impressive from an ingredient quality standpoint — both rely on corn and wheat fillers that cats don't need. If you're willing to spend at this price point, foods like Blue Buffalo (B/76) offer even better ingredients.
Read our full reviews of Hill's Science Diet and Royal Canin for the complete ingredient breakdowns.