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The short answer: Hill's Science Diet wins by a full grade, scoring 76 to Royal Canin Medium Adult's 58 — an 18-point gap (B vs C). The difference comes down to one fundamental issue: Hill's puts chicken first (a protein), while Royal Canin puts brewers rice first (a grain). Both brands are vet-recommended and premium-priced, but Hill's delivers meaningfully better ingredients for the money.

The scores

Royal Canin Medium Adult: C grade, 58/100

Hill's Science Diet Adult: B grade, 76/100

Hill's lands in the B tier; Royal Canin Medium Adult sits a full grade back at the low end of C — well above bottom-tier options like Purina Dog Chow (D/39), but trailing Hill's by 18 points on ingredient quality. For two foods that often sit side by side on vet clinic shelves at similar prices, that's a real and meaningful 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 meaningfully better, which is reflected directly in the 18-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 Medium Adult (C/58) and Hill's Science Diet (B/76) for a healthy adult dog, Hill's is the clear winner on ingredients — a full grade higher, an 18-point gap. Royal Canin's chief draw is its breed- and condition-specific veterinary lineup, not its baseline ingredient quality.

That said, Royal Canin Medium Adult is still a C-grade food at a premium price. For the same money — or less — Kirkland Signature (B/78) and Diamond Naturals (B/78) edge even Hill's while costing significantly less per pound, and both clear Royal Canin Medium Adult by a full grade.