Onion and garlic toxicity calculator for dogs

How much onion is toxic to dogs?

Onions, garlic and their relatives contain sulfur compounds that turn into oxidants in the body. Dogs' red blood cells have weak defenses against oxidants, so the compounds damage them: the cells form clumps called Heinz bodies, break apart, and the dog becomes anemic. Two published figures guide vets:

• 5 g per kg (0.5% of body weight) eaten at one time: the level above which onion poisoning is consistently seen, according to a peer-reviewed veterinary toxicology brief.
• 15 to 30 g per kg of raw onion: the range at which dogs have developed clinical signs, per the Merck Veterinary Manual.

For a 50 lb dog, 0.5% of body weight is about 113 g of onion, about 1 medium onions. Neither figure is a safe line. Damage also builds up when a dog eats smaller amounts day after day, and dogs with an inherited red blood cell trait, relatively common in Japanese breeds such as the Akita and Shiba Inu, are more sensitive.

Is garlic worse than onion for dogs?

Yes. Merck puts garlic at 3 to 5 times as toxic as onion, and the calculator uses the higher end (5 times) so it won't underestimate. Dried forms are stronger still because the water has been removed. Most poisonings in dogs and cats involve concentrated products such as dehydrated flakes, powders and dry onion soup mix.

dose (g/kg) = grams eaten × onion-equivalent factor ÷ dog's weight in kg

Worked example: a 40 lb (18 kg) dog licks up a tablespoon (9.7 g) of garlic powder. That counts as about 110 g of raw onion, or 6 g/kg: past the 0.5% of body weight mark.

Onion and garlic equivalents: raw, cooked and powder

The calculator turns every form into grams of raw onion. Dried forms are converted by dry weight using USDA food composition data, and household measures are USDA weights. This table shows how much of each reaches 0.5% of body weight.

Dry-weight conversion is an estimate: drying may not keep every toxic compound intact, and onions vary. Treat the table as a guide to how concentrated each form is, not a list of safe amounts.

Symptoms of onion and garlic poisoning

The signs come from anemia, and they are usually delayed. After a very large amount, a dog can show signs within a day, but more often there is a gap of several days before the red blood cell count bottoms out. Watch for:

• tiredness, weakness and not wanting to exercise
• pale or yellowish gums
• fast breathing and a fast heartbeat
• red-brown urine (hemoglobin in the urine)
• poor appetite, belly pain, diarrhea, and breath that smells of onion or garlic soon after eating

What to do if your dog ate onion or garlic

1. Remove the rest of the food and check the recipe or label for onion or garlic powder, flakes or soup mix.
2. Call your vet or a poison hotline: ASPCA Animal Poison Control at (888) 426-4435 or Pet Poison Helpline at (855) 764-7661. Both may charge a fee.
3. If it was eaten within the last 1 to 2 hours and your dog is acting normally, the vet may make it vomit. Only do that at home on a vet's instruction; the hydrogen peroxide calculator explains the dose and when never to try it.
4. Expect blood tests over the following days, since that is when anemia appears. Severely affected dogs may need a blood transfusion and oxygen.

There is no antidote, so early decontamination and monitoring are what help. For other foods, check our is it toxic to dogs checker; for takeout snacks in particular, our post on crab rangoon and dogs covers the green onion and garlic that often hide in the filling.