Onion & Garlic Toxicity Calculator for Dogs and Cats
Onion, garlic, leeks and chives damage red blood cells in dogs and cats. Enter what your pet ate to see it as a share of body weight, compared with the levels in the Merck Veterinary Manual.
Enter your pet's weight and the amount eaten. Anemia from onion or garlic usually shows up 1–5 days after eating, so a pet that looks fine today may not be fine on Thursday.
Small amounts add up: the cumulative effect
Allium compounds (such as n-propyl disulfide and thiosulfates) oxidise haemoglobin, forming clumps called Heinz bodies that make red blood cells fragile. The body replaces them slowly, so a little garlic in food every day can do as much damage as one large meal. Step through a week of "just a little" table scraps.
Dog: 20 lb
By day 7 a 20 lb dog has eaten 1.93% of its body weight in onion-equivalent, past the level where toxicosis is consistently reported.
Can dogs eat garlic?
No. Garlic is in the same plant family as onion and is roughly three to five times as potent by weight. Some pet products advertise garlic as a flea remedy; there is no good evidence it works, and the ASPCA lists garlic as toxic to dogs and cats. Powders and dehydrated flakes are the most concentrated forms, which is why gravy, seasoning mixes, baby food and garlic bread cause many cases.
Signs to watch for (1–5 days after)
- Weakness, tiredness, not wanting to walk
- Pale, yellow or brown gums
- Fast breathing or fast heart rate
- Red or brown urine
- Early on: vomiting, drooling, belly pain
Cats and Japanese breeds such as Akitas and Shiba Inus are more sensitive. Your vet may recheck a blood count over several days even if your pet looks well.
Questions owners ask
How much onion is toxic to a dog?
The Merck Veterinary Manual notes onion toxicosis is consistently seen when animals eat more than 0.5% of their body weight in onion at one time, and clinically important blood changes in dogs at 15–30 g/kg. For a 30 lb (13.6 kg) dog, 0.5% is about 68 g: roughly two-thirds of a medium onion.
My dog ate food cooked with onion. Is that dangerous?
A little onion in a large dish is usually a small dose, but powders, gravies and repeated scraps add up. Estimate the onion content with the calculator and call your vet if you are unsure.
How long after eating onion will a dog get sick?
Stomach upset can happen within a day, but anemia typically develops 1–5 days later. Watch for weakness, pale gums or dark urine.
Is garlic worse than onion for dogs?
Yes. Garlic is considered about three to five times as toxic as onion by weight. This calculator uses the cautious end (five times).
Are cats more sensitive to onion than dogs?
Yes. Cats form Heinz bodies more easily; Merck reports important changes from about 5 g/kg of onion in cats. Any notable exposure in a cat deserves a vet call.