The scores
Royal Canin Medium Adult: D grade, 50/100
Hill's Science Diet Adult: C grade, 61/100
This is the widest gap of any comparison we've done between two vet-recommended brands. Royal Canin sits in D territory — the same grade range as Purina Dog Chow — while Hill's earns a solid C. For two foods that often sit side by side on vet clinic shelves at similar prices, that's a significant difference.
How the ingredients compare
Here are the top five ingredients side by side:
Royal Canin: Brewers Rice, Chicken By-Product Meal, Oat Groats, Wheat, Corn Protein Meal
Hill's Science Diet: Chicken, Cracked Pearled Barley, Brown Rice, Brewers Rice, Whole Grain Wheat
The contrast is stark. Hill's leads with chicken — an actual named protein source — followed by whole grains that at least retain some nutritional value. Royal Canin leads with brewers rice, a grain processing byproduct, followed by chicken by-product meal in second place. When a grain byproduct outweighs all protein sources in a premium dog food, that's a red flag.
Where Hill's Science Diet pulls ahead
Chicken as the first ingredient is the single biggest advantage. It means the formula contains more protein from a named animal source by weight than anything else. Hill's also uses more nutritious grain choices — cracked pearled barley and brown rice retain more fiber and micronutrients than Royal Canin's brewers rice and oat groats.
Hill's includes fish oil as an omega-3 source, which supports skin, coat, and joint health. The overall protein-to-carbohydrate balance is simply better, which is reflected directly in the 11-point scoring gap. Shop on Amazon →
Where Royal Canin holds its own
Royal Canin's strength has never been its ingredient list — it's the brand's extensive lineup of breed-specific and condition-specific formulas. If your vet has recommended a specific Royal Canin veterinary diet for a diagnosed medical condition (kidney disease, food allergies, GI issues), those therapeutic formulas are specifically designed for those purposes and may be worth using regardless of the ingredient score.
Royal Canin also includes L-carnitine, which supports fat metabolism and can help with weight management. The oat groats in the formula provide a reasonable source of soluble fiber. And the brand invests heavily in feeding trials and clinical research, which some owners and veterinarians value beyond what ingredient analysis alone can capture. Shop on Amazon →
The bottom line
If you're choosing between Royal Canin (C/58) and Hill's Science Diet (C/61) for a healthy adult dog, Hill's is the clear winner on ingredients. An 11-point gap and a full letter grade difference make this one of the more decisive comparisons in the vet-recommended category.
That said, both are still C and D grade foods at premium prices. For the same money — or less — you could feed Kirkland Signature (B/78) or Diamond Naturals (B/78), both of which outscore Hill's by a full grade while costing significantly less per pound.