Onion & Garlic Toxicity Calculator
Convert onion, garlic, leek, shallot or powdered seasoning into an onion-equivalent dose and compare it against the thresholds for dogs and cats.
Last reviewed July 2026 · Free · Nothing you enter is stored
Allium poisoning is delayed — a normal-looking pet today tells you nothing.
Red blood cell damage typically shows up one to five days after the meal. Call your
veterinarian, the ASPCA Animal Poison Control Center at (888) 426-4435, or the Pet Poison
Helpline at (855) 764-7661 today rather than waiting to see what happens.
What alliums actually do
Onions, garlic, leeks, shallots, and chives all belong to the genus Allium, and they all contain organosulphur compounds — chiefly N-propyl disulphide — that dogs and cats cannot process the way people do. Once absorbed, these compounds oxidise the haemoglobin inside red blood cells. The damaged haemoglobin clumps into deposits called Heinz bodies, the spleen recognises the affected cells as defective, and it removes them from circulation. Enough cells removed, and the animal becomes anaemic.
Two features make this different from most poisonings. The first is the delay: the cells are damaged at the time of the meal but destroyed over the following days, so signs surface one to five days later, long after an owner has stopped worrying. The second is that the dose accumulates. A pet given a little onion-containing food every day can arrive at a toxic total without any single meal being alarming.
Relative potency
This calculator converts everything to onion-equivalent grams, because the thresholds in the veterinary literature are expressed in fresh onion. These are the conversion factors it uses:
| Form | Onion equivalent | Notes |
|---|
| Fresh onion | ×1 | The reference. Toxicity is consistently seen above about 0.5% of body weight eaten at once. |
| Shallot | ×1.2 | Slightly more concentrated than onion, and small enough that a dog may eat several. |
| Leek and scallion | ×0.8 | Milder by weight, but leeks are large — one leek is most of a small onion. |
| Fresh garlic | ×5 | Roughly five times more potent than onion gram for gram. |
| Onion powder | ×8 | Dehydrated and ground. A teaspoon carries as much as a small chunk of raw onion. |
| Garlic powder | ×40 | The most concentrated common form by a wide margin, and the easiest to underestimate. |
Potency ratios derived from Merck Veterinary Manual guidance and published organosulphur content by species and preparation.
The two powder rows are the ones that catch people out. A teaspoon of garlic powder weighs under three grams and looks trivial next to a whole onion, but at forty times the potency it carries the equivalent of about 110 grams of fresh onion — a medium onion, from a spoonful of seasoning.
Thresholds by species
| Onion-equivalent dose | Dogs | Cats, Akitas, Shiba Inus |
|---|
| Watch — subclinical red cell changes possible | 2.5 g/kg | 1 g/kg |
| Concerning — measurable damage likely | 5 g/kg (0.5% of body weight) | 2.5 g/kg |
| Serious — haemolytic anaemia expected | 15 g/kg | 7.5 g/kg |
Dog thresholds anchor on the Merck Veterinary Manual figure of 0.5% of body weight; feline and Japanese-breed thresholds are set at roughly half to reflect their documented red cell susceptibility.
Where alliums hide
| Source | Why it matters |
|---|
| Baby food (meat varieties) | Onion powder is a routine ingredient, and baby food is a common thing to feed a sick pet. |
| Stock cubes, gravy, and broth | Nearly always contain onion or garlic powder. Broth is frequently poured over kibble. |
| Pizza, curry, stir-fry, pasta sauce | Table scraps and counter-surfing account for most real cases. |
| Garlic bread and seasoned crusts | Concentrated garlic in a food dogs will actively steal. |
| Chinese and Indian takeaway leftovers | Both cuisines use alliums heavily, often as a base for everything on the plate. |
| "Natural" flea supplements with garlic | Marketed for pets, unproven as a flea remedy, and a genuine cumulative risk at daily doses. |
| Dehydrated onion in crisps and snack mixes | Powdered forms concentrate the toxic compounds several-fold. |
| Thanksgiving stuffing and turkey drippings | A predictable seasonal spike in poison control calls. |
Meat-flavoured baby food is worth singling out. It is one of the most frequently recommended foods for a pet that will not eat — soft, palatable, easy to syringe — and most brands include onion powder. Feeding it to a sick animal for several days is a realistic route to a cumulative dose at precisely the moment the animal can least afford it.
What a vet will do
Recent ingestion with no symptoms: decontamination, meaning induced vomiting and activated charcoal. Beyond that, the work is monitoring. A packed cell volume is checked at presentation and repeated over three to five days, because the number that matters is the one measured on day three, not the one on arrival. A blood smear looked at under a microscope for Heinz bodies confirms the mechanism.
Supportive care is fluids and rest. Severe cases — usually a pet that ate a large amount, or a cat — may need a transfusion. There is no antidote, which is the whole reason the timing of the phone call carries so much weight here.
Frequently asked questions
How much onion is toxic to a dog?
The consistent figure in the veterinary literature is 0.5% of body weight eaten at once — about 5 grams per kilogram. For a 30 lb dog that is roughly 70 grams, or one small onion. Damage to red blood cells has been measured at lower doses than that, which is why this calculator flags a watch level at 2.5 g/kg as well.
Is garlic worse than onion for dogs?
Yes, by roughly five times per gram of fresh material. The saving grace is quantity: dogs rarely eat five cloves of raw garlic, whereas they will happily eat a whole onion out of a bin. Garlic powder is a different matter — it is about forty times the potency of fresh onion by weight, so a couple of teaspoons in a dish is a real dose for a small dog.
Why are cats and Akitas more sensitive?
Cat haemoglobin has more sulphydryl groups than dog haemoglobin, which makes feline red blood cells markedly more vulnerable to the oxidative damage that allium compounds cause. Akitas and Shiba Inus carry an inherited trait giving their red cells high potassium and high reduced glutathione, which sounds protective and is the opposite — it makes the cells more susceptible to this particular kind of damage. Both groups are given roughly half the dog threshold here.
What are the symptoms of onion poisoning in dogs?
Vomiting and diarrhoea can appear within a day, but the serious signs are delayed. Haemolytic anaemia typically develops one to five days after the meal: pale or yellow-tinged gums, weakness, rapid breathing, an elevated heart rate, dark red or brown urine, and sometimes collapse. That delay is the trap — owners see a dog that seems fine the next morning and assume it passed.
Is a small amount of garlic in dog food or a supplement dangerous?
The trace amounts used as a flavouring in commercial pet food are below any level associated with harm. Garlic supplements sold as natural flea preventatives are a different question: they deliver a meaningful daily dose, they have never been shown to repel fleas, and cumulative exposure over weeks has produced anaemia in documented cases. There is no good reason to take that trade.
Can cooking make onions safe for pets?
No. The organosulphur compounds responsible survive cooking, drying, and powdering intact. Dehydration in fact makes things worse by removing water and concentrating what remains — which is exactly why powders are the most potent form on the table above.
Merck Veterinary Manual: onion toxicosis is consistently seen in animals ingesting more than 0.5% of body weight in onion at once, about 5 g/kg. Garlic is roughly five times more potent by weight, and dehydrated powders are several times more concentrated than fresh. Cats and Japanese dog breeds such as the Akita and Shiba Inu are more susceptible than average.