Tip: a medium onion is about 110 g; one garlic clove is about 3 g. Dried powders are far more concentrated, so small amounts count.
This is an estimate only, not a diagnosis. Because signs can be delayed for days, when in doubt call your vet or a pet poison helpline.
Why onion and garlic are toxic to pets
Onions, garlic, leeks, chives and shallots (the Allium family) contain compounds that damage red blood cells, leading to a type of anemia. All forms count — raw, cooked, fried, dried and powdered — and powders are the most concentrated. Cats are more sensitive than dogs, and the worrying part is that symptoms can be delayed by several days.
As a rough veterinary guide, measured as grams of onion-equivalent per kilogram of body weight:
- Under ~5 g/kg — lower risk, but worth a call, especially for cats.
- ~5–15 g/kg — red-blood-cell damage becomes likely — call your vet.
- Over ~15 g/kg — significant risk of anemia — treat as an emergency.
Garlic and dried powders are far stronger by weight than fresh onion, so this tool converts everything into an "onion-equivalent" and applies an extra margin for cats. Treat the result as a cautious estimate, not a verdict.
What to do if your pet ate onion or garlic
- Call your vet or a pet poison helpline — don't wait for symptoms, which can take days.
- Note the type (fresh, cooked, powder) and amount eaten, and when.
- Watch for weakness, pale gums, lethargy, and reddish or brown urine.
For full guides, see Can dogs eat onion? and Can dogs eat garlic?