Free dog calculator
Dog Onion & Garlic Toxicity Calculator
This dog onion toxicity calculator turns the onion or garlic your dog ate into grams per kilogram of body weight, the unit the Merck Veterinary Manual uses when it reports signs in dogs at 15 to 30 g/kg of raw onion. Garlic is counted at three to five times the strength of onion.
- Dog dose from Merck, portion weights from USDA FoodData Central
- Shows the math behind every number
- Free, no sign-up or email
This is an estimate built from published veterinary figures, not a diagnosis. If your dog ate onion or garlic, call your vet or ASPCA Animal Poison Control at (888) 426-4435 (a consultation fee may apply).
How the onion calculator works
Onions, garlic, leeks and chives all belong to the Allium family. Merck explains that their compounds damage red blood cells and lead to Heinz body anemia. In dogs, it reports clinical signs after 15 to 30 g/kg of raw onion, and it puts garlic at 3 to 5 times more toxic than onion.
The calculator converts what you enter to grams with USDA FoodData Central portion weights, such as 110 g for a medium onion and 3 g for a garlic clove. It divides by your dog’s weight in kilograms. For garlic it multiplies by 3 and by 5, so you see a range of onion-equivalent doses.
How much onion or garlic reaches 15 g/kg
| Dog | Raw onion at 15 g/kg | In medium onions | Garlic (3 to 5 times stronger) |
|---|---|---|---|
| 11 lb (5 kg) | 75 g | about 0.7 medium onion | 15 to 25 g, or 5 to 8 cloves |
| 25 lb (11.3 kg) | 170 g | about 1.5 medium onions | 34 to 57 g, or 11 to 19 cloves |
The garlic figures are our arithmetic from Merck’s 3-to-5 ratio, not a dose Merck states directly. Powders and dried flakes aren’t in the table at all. Merck says concentrated forms are the ones most often involved, but it gives no conversion, so the calculator won’t guess one.
Kitchen amounts, worked out for a dachshund
Nobody weighs the onion a dog snatched off the cutting board, so we converted everyday amounts with USDA FoodData Central portion weights. The percentage is how much of Merck’s 15 g/kg level that amount reaches. Garlic shows a range because Merck rates it 3 to 5 times stronger than onion.
| Amount | Grams | 11 lb dog | 25 lb dog |
|---|---|---|---|
| 1 tbsp chopped onion | 10 g | 2.0 g/kg (13%) | 0.9 g/kg (6%) |
| 1 medium onion slice | 14 g | 2.8 g/kg (19%) | 1.2 g/kg (8%) |
| 10 raw onion rings | 60 g | 12.0 g/kg (80%) | 5.3 g/kg (35%) |
| 1 small onion | 70 g | 14.0 g/kg (94%) | 6.2 g/kg (41%) |
| 1 medium onion | 110 g | 22.0 g/kg (147%) | 9.7 g/kg (65%) |
| 1 cup chopped onion | 160 g | 32.1 g/kg (214%) | 14.1 g/kg (94%) |
| 1 garlic clove | 3 g | 1.8 to 3.0 g/kg (12 to 20%) | 0.8 to 1.3 g/kg (5 to 9%) |
| 3 garlic cloves | 9 g | 5.4 to 9.0 g/kg (36 to 60%) | 2.4 to 4.0 g/kg (16 to 26%) |
| 1 tsp garlic | 2.8 g | 1.7 to 2.8 g/kg (11 to 19%) | 0.7 to 1.2 g/kg (5 to 8%) |
For an 11 lb miniature, the line arrives at about two-thirds of a medium onion, or five to eight garlic cloves. A dropped slice or a spoonful of chopped onion is well under it. The harder calls are seasoned leftovers and powders, which the table can’t cover.
Onion in leftovers: work it out from the recipe
Most onion questions owners post aren’t about a raw onion. They’re about leftovers: a few bites of a stew, salmon skin from a pan that had onions in it, a plate licked clean. Choose Part of a dish in the calculator, enter the onion that went into the whole recipe, then how many servings it made and how much of one your dog ate.
Here’s a real case from r/PetAdvice. A 13 lb, 10-year-old dog stole a few bites of goulash, about a quarter of a serving by the owner’s estimate. The batch used one onion and made seven servings. At USDA’s 110 g for a medium onion, that’s about 3.9 g of onion, or 0.67 g/kg, roughly 4% of the 15 g/kg level where Merck reports signs. The recipe also used garlic salt, which can’t be counted without an amount, so calling the poison line still made sense. The owner did, and was told to watch for signs of anemia over the following days.
Why the signs come late
- Methemoglobinemia begins, Merck says, and peaks at about 72 hours.
- Red blood cells break down. This is when hemolysis typically happens.
- Lethargy, loss of appetite, fast breathing, weakness, yellow tinge, dark urine or collapse.
A dog that looks fine the evening it ate onion isn’t in the clear yet. Keep watching for several days, and treat cooked onion the same as raw, since Merck lists raw, cooked, dehydrated and granulated forms.
Onion and garlic questions
Is cooked onion safer than raw?
No. Merck reports poisoning in dogs and cats from raw, cooked, dehydrated and granulated onions and garlic. Cooking doesn’t remove the problem.
How much garlic is toxic to a dog?
Merck doesn’t give a garlic dose for dogs. It gives 15 to 30 g/kg for raw onion and says garlic is 3 to 5 times more toxic, which puts garlic somewhere around 3 to 5 g/kg by that ratio. For an 11 lb dog, that’s roughly 5 to 8 cloves.
What about foods seasoned with onion powder?
Seasoned snacks, gravy and soup mixes are the concentrated forms Merck flags. The amount per bite is usually small and unlisted, which is why we read cracker labels flavor by flavor before sharing anything.
Sources
- Merck Veterinary Manual, Garlic and Onion (Allium spp) Toxicosis in Animals: dog dose, garlic ratio, concentrated forms and timing (read October 2026).
- USDA FoodData Central, SR Legacy records 170000 (onions, raw) and 169230 (garlic, raw): portion weights.
- ASPCA Animal Poison Control Center: phone line and fee note (read October 2026).