Onion and Garlic Toxicity Calculator for Dogs
Work out whether the amount of onion, garlic, leek or chive your dog ate reaches the dose that damages red blood cells.
Cooking does not destroy the toxic compounds.
Gastrointestinal upset likely
7.33 g onion equivalent per kg
Vomiting, diarrhea, drooling, abdominal pain and loss of appetite.
Call your vet for advice, and mention exactly what was eaten and when.
- Actual amount eaten
- 110.0 g
- Potency multiplier
- ×1
- Onion equivalent
- 110.0 g
- Amount that would reach the toxic dose
- 225.0 g of this
Effects are cumulative and delayed. Anemia typically develops over one to five days, so a dog that seems fine that evening tells you nothing. Small amounts eaten regularly can add up to the same result as one large meal.
How this is calculated
Different alliums vary in potency, so amounts are converted to an onion equivalent before the dose is banded. Garlic counts for five times its weight, garlic powder twenty-five times.
grams eaten = units × grams per unit
onion equivalent = grams eaten × potency multiplier
dose (g/kg) = onion equivalent ÷ body weight in kg Worked example
A 10 kg dog eats ten garlic cloves. That is 30 g of garlic, which at a potency of five is 150 g of onion equivalent, giving 15 g/kg — right at the threshold where red blood cell damage becomes likely.
Potency by type
| Type | Potency | Typical unit |
|---|---|---|
| Raw onion | ×1 | 110 g per medium onion |
| Cooked onion | ×1 | 80 g per portion |
| Onion powder | ×6 | 2.4 g per teaspoon |
| Garlic clove | ×5 | 3 g per clove |
| Garlic powder | ×25 | 2.8 g per teaspoon |
| Leek | ×1 | 90 g per leek |
| Chives | ×1 | 3 g per tablespoon |
Dose thresholds
| Dose | Effect | Expected signs |
|---|---|---|
| under 5 g/kg | Below the reported threshold | Significant red blood cell damage is unlikely at this dose. Stomach upset is still possible. |
| 5+ g/kg | Gastrointestinal upset likely | Vomiting, diarrhea, drooling, abdominal pain and loss of appetite. |
| 15+ g/kg | Red blood cell damage likely | Heinz-body anemia developing over one to five days: lethargy, weakness, pale or yellow gums, fast breathing, and sometimes red-brown urine. |
| 30+ g/kg | Severe anemia risk | Marked hemolytic anemia, collapse, and in serious cases a need for blood transfusion. |
Sources
What actually happens
Organosulfur compounds in alliums oxidize hemoglobin, forming clumps called Heinz bodies. The spleen removes the damaged cells, and if enough are damaged the dog becomes anemic. Because this takes days to build, the timeline of a poisoning does not match what owners expect.
Where it usually comes from
Rarely a dog eating a raw onion. Far more often leftovers: gravy, stuffing, curry, pizza, bolognese, fried rice, baby food, or bouillon cubes used to make a bland diet more appealing. Onion powder in particular hides in things that do not taste of onion at all.
When you describe what happened to a vet, describe the dish rather than the ingredient, and take the packet if there was one.
Common questions
How much onion is toxic to a dog?
Clinically significant red blood cell damage generally needs about 15 to 30 g of onion per kilogram of body weight. For a 15 kg dog that is roughly 225 to 450 g, or two to four medium onions. Smaller amounts can still cause stomach upset.
Is garlic worse than onion for dogs?
Yes, about five times more potent by weight, because it contains more of the organosulfur compounds responsible. Garlic powder is more concentrated again, at roughly 25 times the potency of fresh onion gram for gram.
Is a small amount of garlic safe for dogs?
A tiny amount in a cooked meal is unlikely to harm a medium or large dog on a single occasion. That is not the same as safe. Effects are cumulative, small dogs have far less margin, and there is no established benefit to offset the risk, so the sensible position is to avoid it.
Does cooking destroy the toxin?
No. Cooking, drying and powdering all leave the toxic compounds intact, and drying concentrates them. Cooked onion in gravy, stuffing, curry or leftovers is exactly as dangerous as raw.
What are the symptoms of onion poisoning in dogs?
Stomach upset first: vomiting, diarrhea, drooling and abdominal pain. Then, over one to five days, the signs of anemia: lethargy, weakness, pale or yellow gums, fast breathing, and sometimes red or brown urine.
My dog ate onion days ago and seems fine. Is it over?
Not necessarily. The anemia is delayed and often peaks three to five days after ingestion. If the calculated dose was in the toxic range, blood tests are still worth doing even in a dog that looks well.
Does garlic repel fleas?
There is no good evidence that it does, and there is clear evidence that it is toxic. Supplements marketed on this basis are not worth the risk when effective, safe flea treatments exist.