What this calculator does
Onions, along with other allium plants such as garlic, leeks and chives, contain thiosulphates and related compounds (including N-propyl disulphide) that damage a dog’s red blood cells and can cause a form of anaemia. Cooking does not reliably remove this risk, and dehydrated or powdered onion is considerably more concentrated, gram for gram, than raw onion.
This calculator gives a rough estimate of how much onion a dog has eaten, in grams per kilogram of body weight, checked against toxicity thresholds commonly cited in veterinary references, roughly around 15 to 30 g/kg of body weight for clinical effects to appear. It is an educational estimate only, not a diagnosis, and it does not replace contacting a vet or an animal poison control line, which you should do regardless of what this estimate shows if you are worried.
The formula
The amount of onion eaten is multiplied by a concentration factor for the form it was eaten in (dehydrated or powdered onion is treated as several times more concentrated than raw or cooked onion, since it is much less diluted by water), giving a raw-onion-equivalent total. That total is divided by the dog’s body weight to give a dose in grams per kilogram, which is then compared against the published reference thresholds.
| Term | Meaning |
|---|---|
| Dose (g/kg) | Total onion eaten (raw-equivalent), divided by body weight, the unit the published thresholds are expressed in. |
| Raw-onion-equivalent | The amount eaten adjusted for how concentrated that form of onion is compared with fresh raw onion. |
| Toxicity threshold | Roughly 15–30 g/kg of body weight is often cited in veterinary references as the range where clinical signs of onion toxicity can begin to appear. |
| Cumulative exposure | Repeated smaller amounts of onion eaten over several days can add up to a toxic total dose, even if no single serving looks large on its own. |
The inputs explained
| Field | What to enter |
|---|---|
| Form of onion eaten | Whether the onion eaten was raw or cooked, or a more concentrated dehydrated or powdered form, such as found in some seasonings, stocks or processed foods. |
| Amount eaten (g) | The actual amount of onion (in that form) eaten. |
| Dog's weight (kg) | The dog's body weight. |
When to use it
A dog has gotten into onions or a dish containing them
Working out an approximate dose per kilogram gives a rough sense of how much of a concern it is while you contact a vet or poison control line, not a substitute for making that call.
Checking a seasoning or stock cube ingredient
Dehydrated onion and onion powder, common in stock cubes, gravies and packaged seasonings, are far more concentrated per gram than raw onion, so a small amount of a seasoned dish can matter more than it looks.
Weighing up a smaller dog against a larger one
The same amount of onion produces a much higher dose per kilogram in a small dog than in a large one, which is why body weight, not just the amount eaten, has to be part of the estimate.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How estimated dose changes with a dog’s weight, for the same amount eaten
A fixed 100 g of raw onion, eaten by dogs of different weights.
| Dog's weight | Estimated dose (raw-onion-equivalent) | Risk level |
|---|---|---|
| 5 kg | 20.0 g/kg body weight | Within the commonly cited toxic range: contact a vet |
| 10 kg | 10.0 g/kg body weight | Below the commonly cited toxicity threshold, but no amount of onion is a safe treat, and repeated small amounts can add up over several days |
| 15 kg | 6.7 g/kg body weight | Below the commonly cited toxicity threshold, but no amount of onion is a safe treat, and repeated small amounts can add up over several days |
| 20 kg | 5.0 g/kg body weight | Below the commonly cited toxicity threshold, but no amount of onion is a safe treat, and repeated small amounts can add up over several days |
| 30 kg | 3.3 g/kg body weight | Below the commonly cited toxicity threshold, but no amount of onion is a safe treat, and repeated small amounts can add up over several days |
How estimated dose changes between raw and concentrated onion
The same 30 g eaten, once as raw or cooked onion and once as dehydrated onion or onion powder.
| Form eaten | Estimated dose (raw-onion-equivalent) | Total onion eaten (raw-equivalent) |
|---|---|---|
| Raw or cooked | 2.0 g/kg body weight | 30 g |
| Dehydrated / powdered | 10.0 g/kg body weight | 150 g |
Questions
How much onion is toxic to dogs?
Veterinary references commonly cite a range of roughly 15 to 30 g of onion per kilogram of a dog’s body weight as the dose at which clinical signs can start to appear, though individual sensitivity varies and there is no dose that is guaranteed safe. This calculator estimates where a given amount and body weight fall against that range, not a precise personal threshold.
Does cooking onion make it safe for dogs?
No. Cooking does not reliably destroy the compounds in onion responsible for the toxic effect, so cooked onion (in gravies, soups or leftovers, for example) still carries the same underlying risk as raw onion.
Is a small amount of onion in a meal actually dangerous?
A single small taste is less likely to reach a toxic dose than a large deliberate serving, but repeated small amounts over several days can accumulate toward a toxic total, and there is no established fully safe amount. If there is any doubt, contact a vet rather than assuming it is fine.
What should I do if my dog has eaten onion?
Contact a vet or an animal poison control line, and have the approximate amount and form of onion eaten (raw, cooked, or powdered/dehydrated) along with the dog’s weight ready to describe. Do not wait for symptoms to appear before calling, since earlier treatment is more effective.
For the equivalent question about chocolate, see the dog chocolate toxicity calculator. For everyday feeding amounts once the immediate concern has passed, see the dog daily food amount calculator.