How the dose is calculated
Onion, garlic, leeks, shallots and chives (the Allium family) contain sulfur compounds that damage red blood cells. The damaged cells are destroyed, which causes anemia. The calculator converts what was eaten into grams of onion per kilogram of your pet's weight, counting garlic as five times stronger.
Onion-equivalent (g/kg) = grams eaten × strength ÷ pet's weight (kg)
Strength: onion = 1, garlic = 3 to 5 (we use 5)
1 oz = 28.35 g, 1 lb = 0.4536 kg
Worked example: a 44 lb dog eats 4 oz of onion
44 lb is 19.96 kg and 4 oz is 113.4 g, so the dose is 113.4 ÷ 19.96 = 5.7 g/kg. That is above the 0.5%-of-body-weight level the ASPCA's poison control center linked to onion toxicity in dogs, though below Merck's 15–30 g/kg range for clinical signs. If the same dog ate 1 oz (28.35 g) of garlic instead, that counts as 28.35 × 5 = 141.75 g of onion, or 7.1 g/kg (4.3 g/kg at the ×3 end).
Levels the calculator uses
| Pet | Onion-equivalent dose | What has been reported |
|---|---|---|
| Dog | 5 g/kg (0.5% of body weight) | Toxicity in an early study; poison-control cases with signs were all above this |
| Dog | 15–30 g/kg | Clinical signs (Merck) |
| Cat | 5 g/kg raw onion | Toxicosis (Merck) |
| Cat | Less than a teaspoon of cooked onion | Reported poisoning (Merck) |
Sources: the Merck Veterinary Manual chapter written by an ASPCA Animal Poison Control Center veterinarian (reviewed September 2024), and the ASPCA poison control toxicology brief on onions (2001). Some dogs, including Akitas and Shiba Inus, inherit red blood cells that are more easily damaged, so treat any result as a reason to call.
Powders, mixes and repeat exposure
Dried onion and garlic are far more concentrated than fresh, and seasoning mixes vary, so the calculator does not turn them into a number. Choose that option and it will simply tell you to call. Merck does not give a figure for small amounts eaten over several days. If your pet has had food with onion or garlic on more than one day, tell your vet the total.
What happens next
- Vomiting, diarrhea or loss of appetite can come early. Signs of anemia (weakness, pale or yellow gums, fast breathing, red or brown urine) usually take a few days; Merck says the red cell damage typically peaks 3 to 5 days after eating.
- If it was eaten recently, a vet may make your pet vomit. Do not do this at home unless a vet or poison line tells you to.
- Vets often recheck the red blood cell count over several days.
Phone numbers and fees were checked on the ASPCA and Pet Poison Helpline websites in October 2026.
Questions people ask
How much onion is toxic to a dog?
The Merck Veterinary Manual reports clinical signs in dogs after 15 to 30 g of raw onion per kg of body weight. An older ASPCA poison control review found toxicity above 0.5% of body weight (5 g/kg), and the dogs that showed signs had all eaten more than that. For a 20 kg (44 lb) dog, 5 g/kg is 100 g (3.5 oz) of onion.
Is garlic worse than onion?
Yes. Merck says garlic is roughly 3 to 5 times as toxic as onion. The calculator multiplies garlic by 5 to err on the side of caution and also shows the ×3 figure.
Are cats more sensitive than dogs?
Much more. Cat hemoglobin is especially easy to damage by oxidation. Merck reports poisoning in cats after 5 g/kg of raw onion, and after less than a teaspoon of cooked onion. Concentrated forms such as onion powder, dried flakes and soup mixes are the usual culprits in cats.
Does cooking make onion safe?
No. Raw, cooked, dried and powdered onion and garlic have all poisoned dogs and cats. Cooking does not remove the compounds that damage red blood cells. Gravy, stock, baby food and seasoned leftovers often contain onion or garlic powder.
How long until symptoms show?
Usually a few days. Merck says the red blood cell damage (hemolysis) typically peaks 3 to 5 days after eating, and signs of anemia can take several days to appear. Vomiting, diarrhea or loss of appetite may come sooner. A pet that seems fine on day one is not in the clear.
Do the poison hotlines charge?
Pet Poison Helpline lists an $89 per-incident fee that includes follow-up calls. The ASPCA Animal Poison Control Center says a consultation fee may apply. Both answer 24 hours a day, every day.