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Brand Comparison · 2026

Iams vs Kirkland Signature

Iams (mass-market-priced kibble from a maker that meets 4 of WSAVA's 5 questions, for budget-conscious owners) and Kirkland Signature (Costco's private-label dry food, reportedly made by Diamond Pet Foods, which meets 2 of WSAVA's 5 questions) compared head-to-head on WSAVA manufacturer-quality criteria, AAFCO substantiation, monthly cost, and which dog each is best for in 2026. Iams meets 4 of 5 WSAVA criteria. Kirkland Signature is roughly 43% less than Iams.

The verdict

Iams has the better paper trail of these two budget kibbles. It meets 4 of 5 WSAVA questions at $25-45/month, backed by PhD nutrition scientists Mars Petcare has named on record. Kirkland Signature meets 2 of 5 at about $20 a month. Neither label cites feeding trials, since both say "formulated to meet" AAFCO profiles. Diamond, the reported maker of Kirkland Signature, names no one.

Iams costs $5 to $25 more a month, which is the whole price of the extra evidence. Pick Kirkland Signature if you shop at Costco and the bill matters most. Pick Iams if you want a parent company with PhD nutrition staff on record, and note that its prescription line is limited. A veterinarian should guide any dog with allergies or health issues.

Key differences at a glance

Quick comparison

DimensionIamsKirkland Signature
Parent companyMars IncorporatedCostco (reportedly made by Diamond Pet Foods)
CategoryMass-market dry kibbleMass-market dry kibble
WSAVA criteria met4 of 52 of 5
AAFCO substantiationFormulation onlyFormulation only
Full-time veterinary nutritionistYesPartial
Credentialed formulatorYesPartial
AAFCO feeding trialsNoNo
Owns manufacturing plantsYesYes
Quality control programYesYes
Typical monthly cost (50 lb dog)$25 – $45 / month$20 / month

Mars Incorporated

Iams

Mass-market-priced kibble from a maker that meets 4 of WSAVA's 5 questions, for budget-conscious owners.

Strengths

  • Low price from a maker that meets 4 of WSAVA's 5 manufacturer questions
  • Same manufacturing-control standards as Eukanuba and Royal Canin
  • Wide retail availability (grocery and pet stores)

Watch-outs

  • Limited prescription-diet line; pair with another brand if therapeutic diet is needed
  • Flagship label says "formulated to meet" AAFCO profiles rather than citing feeding trials
  • Ingredient list is more mass-market-tier than Pro Plan

Best for: Healthy adult dogs on a tight budget whose owners still want a maker that meets 4 of WSAVA's 5 questions.

Avoid if: You have a dog with allergies or want a premium-tier ingredient profile.

Visit Iams ↗

Costco (reportedly made by Diamond Pet Foods)

Kirkland Signature

Costco's private-label dry food, reportedly made by Diamond Pet Foods, which meets 2 of WSAVA's 5 questions.

Strengths

  • Low price, about $1 a pound for the 25 lb bag, or roughly $20 a month for a 50 lb dog
  • Diamond, the reported maker, publishes a test-and-hold program with certified-lab testing
  • Diamond operates seven US manufacturing facilities and is family-owned

Watch-outs

  • Costco's product page names no manufacturer. Costco's 2025 pet FAQ said Diamond makes the dry foods, but the bag's own maker line was not checked
  • Label says "formulated to meet" AAFCO profiles rather than citing feeding trials
  • No named nutritionist or formulator. Diamond describes only unnamed experts
  • Costco's Nature's Domain grain-free line was named in 29 reports in the FDA's 2019 DCM update. The FDA did not establish that any food caused the disease

Best for: Costco members who want a low-cost dry food and will check the bag's manufacturer line themselves.

Avoid if: You want a named, credentialed nutrition team or feeding-trial substantiation behind the food.

Visit Kirkland Signature ↗

Which is better for your dog?

The right pick depends on your individual dog. Iams is the better choice when: Healthy adult dogs on a tight budget whose owners still want a maker that meets 4 of WSAVA's 5 questions. Kirkland Signature is the better choice when: Costco members who want a low-cost dry food and will check the bag's manufacturer line themselves.

On cost, Kirkland Signature is roughly 43% less than Iams at the midpoint of typical premium spec for a 50 lb adult dog. On WSAVA manufacturer-quality criteria, Iams meets 4 of 5 vs 2 of 5 for Kirkland Signature.

Checking one brand rather than the pair? See is Iams WSAVA-approved or is Kirkland Signature WSAVA-approved.

Where to buy

Made your pick?

Check current pricing on whichever brand fits your dog. Prices and promotions change frequently, so it is worth comparing both before you commit to a bag or a subscription.

Shop Iams on Chewy →

Disclosure: these are affiliate links and IntelliBowl may earn a commission at no extra cost to you. Commission does not influence the comparison above. See our methodology.

Personalized recommendation

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Compare these brands against others

Methodology: WSAVA criteria reflect each brand's publicly documented manufacturer-quality practices as of October 2026, scored against the WSAVA Global Nutrition Committee's 5-question rubric. AAFCO substantiation reflects the dominant method used across the brand's main retail product line. Monthly cost reflects typical US 2026 retail for a 50 lb adult dog at premium spec, before autoship discounts. Recommendations are editorial and not influenced by affiliate relationships. See our recommendation methodology for IntelliBowl's quiz-engine ranking logic.