Onion Toxicity Calculator for Dogs
Merck Veterinary Manual reports signs in dogs after 15–30 g/kg of onion, and a peer-reviewed review notes toxicosis is consistently seen when a dog eats more than 0.5% of its body weight in onion at one time. (Merck Veterinary Manual; Salgado BS, Monteiro LN, Rocha NS. Allium species poisoning in dogs and cats. J Venom Anim Toxins incl Trop Dis. 2011;17(1):4-11.)
Onion toxicity calculator
Educational estimate from published toxicology references. Not veterinary advice. If in doubt, call your vet.
Unit weights are approximate (USDA FoodData Central reference weights); real sizes vary.
Risk level (example)
Monitor (lower risk)
Estimated dose: 1.03 g/kg
Form: raw onion (×1 vs fresh onion) — 14 g eaten ≈ 14 g fresh-onion equivalent.
- Watch for weakness, pale gums, red-brown urine or fast breathing for several days.
- Signs can be delayed 1–5 days; call your vet if any appear.
- Note the product, amount and time eaten; keep the packaging.
Emergency line
ASPCA APCC (888) 426-4435, fee may apply · Pet Poison Helpline (855) 764-7661, fee may apply
How thresholds are set: Merck reports signs in dogs after 15–30 g/kg of raw onion, and Salgado et al. (2011) note toxicosis is consistently seen above 0.5% of body weight (5 g/kg) eaten at one time. Powder and dried flakes are converted to fresh-onion equivalent using USDA FoodData Central dry matter (powder ×8.7, flakes ×8.8). Repeated small exposures can cause harm at lower amounts, so they raise the risk level by one step.
Source: Merck Veterinary Manual — garlic and onion (Allium) toxicosis; Pet Poison Helpline — onions
Educational estimate from published toxicology references. Not veterinary advice. If in doubt, call your vet.
Garlic
Garlic is 3–5 times more toxic than onion (Merck Veterinary Manual), but no validated dose threshold for dogs is published. Treat any garlic, especially powder or supplements, as a reason to call your vet or poison control.
Higher-risk breeds
Japanese breeds such as the Akita and Shiba Inu are reported to be more sensitive to onion toxicity, because some have red blood cells with high potassium and reduced glutathione (Salgado et al. 2011). Contact your vet at lower amounts for these breeds.
Result tiers and what to do now
Monitor (lower risk) — Below ~5 g/kg
Watch for weakness, pale gums, red-brown urine or fast breathing for several days; signs can be delayed 1–5 days. (Pet Poison Helpline)
Call your vet — ~5–15 g/kg (≥ 0.5% body weight)
Call your vet; blood checks for anemia may be suggested. (Salgado BS, Monteiro LN, Rocha NS. Allium species poisoning in dogs and cats. J Venom Anim Toxins incl Trop Dis. 2011;17(1):4-11.)
Call your vet now — ≥ ~15 g/kg
Call your vet or a poison hotline right away. (Merck Veterinary Manual)
Call for help
Call your vet or an emergency clinic. ASPCA Animal Poison Control Center (888) 426-4435 or Pet Poison Helpline (855) 764-7661 (fees may apply). Never induce vomiting without a vet's say-so.
Dose by dog weight
| Dog weight | 0.5% body weight (5 g/kg) | 15 g/kg (Merck, low end) |
|---|---|---|
| 5 lb (2.3 kg) | 11 g | 34 g |
| 10 lb (4.5 kg) | 23 g | 68 g |
| 20 lb (9.1 kg) | 45 g | 136 g |
| 40 lb (18.1 kg) | 91 g | 272 g |
| 80 lb (36.3 kg) | 181 g | 544 g |
Cooking does not destroy the toxic compounds (Merck), so raw and cooked onion count the same by weight. Onion powder and dried flakes are far more concentrated: the calculator converts them to fresh-onion equivalent using USDA FoodData Central dry matter (powder ×8.7, flakes ×8.8). Spoon measures use USDA portion weights: powder 1 tsp = 2.4 g and 1 tbsp = 6.9 g; flakes 1 tbsp = 5.0 g. Repeated small exposures also add up. Published ranges are not safe allowances.
Frequently asked questions
How much onion is toxic to a dog?
Merck reports signs after 15–30 g/kg of onion, and Salgado et al. (2011) note toxicosis is consistently seen above 0.5% of body weight eaten at one time. Repeated small amounts can also cause harm.
Is cooked onion safe for dogs?
No. Cooking, drying or frying does not remove the compounds that damage red blood cells, so cooked onion counts the same by weight.
Is garlic worse than onion?
Yes. Merck reports garlic is roughly 3–5 times as potent as onion by weight. Use the garlic guide rather than this calculator for garlic.
When do onion poisoning signs appear?
Anemia signs such as weakness, pale gums and dark urine are often delayed 1–5 days, so call your vet even if your dog seems normal.
Full guide: symptoms, timeline, treatment & cost
Garlic is about 3–5× more toxic than onion (Merck) — read the garlic guide
Related calculators
Sources
- Merck Veterinary Manual — garlic and onion (Allium) toxicosis
- Salgado BS, Monteiro LN, Rocha NS. Allium species poisoning in dogs and cats. J Venom Anim Toxins incl Trop Dis. 2011;17(1):4-11.
- Pet Poison Helpline — onions
- USDA FoodData Central — raw onion (FDC 170000), onion powder (FDC 171327; 1 tsp = 2.4 g, 1 tbsp = 6.9 g), dehydrated onion flakes (FDC 170002; 1 tbsp = 5.0 g)
Educational estimate from published toxicology references. Not veterinary advice. If in doubt, call your vet.