The figure most often cited is onion at or above roughly 0.5% of a dog's body weight in a single meal, which is about 45 g for a 20 lb dog. Garlic is several times more potent by weight, at around 1 g per kilogram. Two things matter more than the numbers: dried onion and onion powder are far more concentrated than fresh, and the signs are delayed by one to five days, so a dog that seems fine tonight has not been cleared.
The number, by your dog's weight
Start here, because it is the question you came for. The threshold usually quoted for onion is 0.5% of body weight eaten at once, which works out to 5 g of onion per kilogram of dog. Garlic is reported to be considerably more potent for the same mass, and the figure commonly cited sits around 1 g per kilogram.
Find your dog's weight on the charts below and read across. A 10 lb terrier reaches the onion line at roughly 23 g, which is about a slice and a half of raw onion. A 50 lb Labrador reaches it at roughly 113 g, which is most of a medium onion. That difference is the entire reason a single sentence about onions being toxic is useless to either owner.
- High risk
- Never
Horizontal: body weight, 5 to 120 lb. Vertical: Onion (grams). Each sloping line is a published threshold, so it sits higher for a heavier dog.
- At or above 0.5% of body weight — a 20 lb dog reaches this at 45 g.
- For scale: One slice of raw onion is about 15 g. Basis: typical 1/8 inch slice of a medium onion, recipe-derived.
- For scale: One teaspoon onion powder, as fresh-onion equivalent is about 20 g. Basis: a level teaspoon is about 2.4 g of powder, and drying removes most of the water, so it stands in for roughly 20 g of fresh onion. This is an estimate for scale, not a published equivalence.
View as table
| Dog weight | Reaches 0.5% of body weight |
|---|---|
| 10 lb | 23 g |
| 20 lb | 45 g |
| 30 lb | 68 g |
| 50 lb | 113 g |
| 80 lb | 181 g |
Source: Merck Veterinary Manual and ASPCA Animal Poison Control Center
- High risk
- Never
Horizontal: body weight, 5 to 120 lb. Vertical: Garlic (grams). Each sloping line is a published threshold, so it sits higher for a heavier dog.
- At or above the commonly cited garlic threshold — a 20 lb dog reaches this at 9.1 g.
- For scale: One clove of garlic is about 3.0 g. Basis: typical supermarket clove, 3-7 g; the low end used here.
View as table
| Dog weight | Reaches the commonly cited garlic threshold |
|---|---|
| 10 lb | 4.5 g |
| 20 lb | 9.1 g |
| 30 lb | 14 g |
| 50 lb | 23 g |
| 80 lb | 36 g |
Source: Merck Veterinary Manual and ASPCA Animal Poison Control Center
Garlic is stronger than onion, but sources disagree on how much
Garlic being more potent than onion by weight is consistently reported, and it makes intuitive sense: garlic is denser and its organosulfur compounds are more concentrated per gram. What is not consistent is the multiple. Published figures put garlic somewhere between roughly three and five times the potency of onion for the same mass, and the range is wide enough that you should treat any single number, including ours, as approximate.
Rather than average the range and present a false precision, the curve above is drawn at the conservative end. If you are trying to decide whether an exposure matters, use the lower figure. If you are trying to understand a threshold your vet quoted, expect them to be working from the same imprecise literature.
The same caveat applies to onion itself, and it is worth stating rather than hiding. The 0.5%-of-body-weight figure used above is the conservative end of a published range; higher thresholds appear in the literature too, and you will find both quoted by reputable sources. This page uses the lower one deliberately, because the cost of treating a borderline exposure as real is a phone call, and the cost of the reverse is an anaemic dog several days later.
The mechanism, and why it is delayed
Alliums contain organosulfur compounds, chiefly n-propyl disulfide and various thiosulfates. These oxidise the haemoglobin inside a dog's red blood cells. The damaged haemoglobin precipitates into clumps called Heinz bodies, the spleen and liver recognise those cells as defective, and the cells are cleared from circulation. The result is haemolytic anaemia.
That is a multi-step biological process, not a chemical burn, and it takes time. Signs typically appear one to five days after the meal, not within hours. This single fact is the most important thing on this page, because it inverts the intuition every owner has: with most poisonings, a dog that is bright and well several hours later is reassuring. With allium, it means nothing at all.
What you eventually see is pallor, weakness, lethargy, exercise intolerance, rapid breathing, an elevated heart rate, and in more severe cases dark or red-brown urine as the broken-down cells are excreted. our allium toxicity reference covers the clinical picture and the genus in more depth; this page is the arithmetic that sits beside it.
- Caution
- High risk
- Never
Hours after the dog ate it, from 0 to 96.
View as table
| What | Signs begin | Through | Tier | Note |
|---|---|---|---|---|
| Vomiting or diarrhoea, if any | 2 h | 24 h | ▲ Caution | Simple irritation. Often absent entirely. |
| Heinz bodies forming | 12 h | 72 h | ◆ High risk | Nothing visible. Detectable on a blood smear. |
| Pallor, weakness, fast breathing | 24 h | 96 h | ■ Never | The anaemia becoming apparent. This is the part that matters. |
| Dark or red-brown urine | 36 h | 96 h | ■ Never | Broken-down red cells being excreted. Call now. |
Source: Merck Veterinary Manual and ASPCA Animal Poison Control Center
Powder is not the same as fresh
This is where most accidental exposures actually come from, and it is the part almost no one accounts for. Dehydrated onion and onion powder have had the water removed, so per gram they carry several times the allium load of a raw onion. A level teaspoon of onion powder is only about 2.4 g on the scale, but it stands in for a much larger mass of fresh onion.
The practical consequence is that a teaspoon of Onion Soup Mix stirred into a dip can outweigh the slice of raw onion that fell off the chopping board, and the dip is the one the dog is more likely to get a lot of. The same logic makes Onion Powder, Onion Salt, Dehydrated Onion, Garlic Powder, Garlic Salt and Onion Dip Mix more of a practical hazard than the fresh bulbs they came from.
Why so much of this is invisible on a label is covered in hidden onion and garlic in everyday foods, and the sauce and dressing shelf specifically in hidden allium in sauces and dressings.
- Never
- High risk
- Caution
Measured in index, fresh onion = 1.
View as table
| Item | index, fresh onion = 1 | Tier | Note |
|---|---|---|---|
| Garlic powder | 30 | ■ Never | dried and denser again |
| Onion powder | 8 | ■ Never | the usual culprit |
| Dehydrated onion | 7 | ◆ High risk | |
| Garlic clove, raw | 4 | ◆ High risk | raw and crushed is the strong form |
| Onion, cooked | 1 | ▲ Caution | cooking does not neutralise it |
| Onion, raw | 1 | ▲ Caution |
Source: Estimated from typical moisture-loss ratios for dehydrated alliums. This is a relative index for scale, not a laboratory measurement or a published toxicological figure.
The whole genus counts
Everything in the genus Allium carries the same compounds, so the question is never whether a particular one is safe but how concentrated it is and how much a dog ate. That includes Onion, Garlic, Shallots, Leeks, Chives and Green Onions, along with ramps and scallions, which we do not cover separately because they behave like the others.
Cooking does not solve it. Roasting, frying and simmering change the flavour and soften the texture, but they do not break down the organosulfur compounds in any way that removes the risk. A dog that ate Fried Onions off a burger or the onion out of French Onion Soup has had a real exposure, and it is judged on the same weight-based threshold as raw onion.
| Allium | Form | Relative potency | Where dogs meet it |
|---|---|---|---|
| Onion | Fresh bulb | Baseline | Chopping board, burgers, stews |
| Onion Powder | Dried | Much higher per gram | Seasoning blends, crisps, canned meals |
| Garlic | Fresh clove | Several times onion | Sauces, garlic bread, roast dinners |
| Garlic Powder | Dried | Highest per gram | Rubs, seasoned fries, snack coatings |
| Shallots | Fresh bulb | Comparable to onion | Dressings, pan sauces |
| Leeks | Fresh stem | Comparable to onion | Soups, braises |
| Chives | Fresh herb | Comparable to onion | Garnish, Chive Cream Cheese |
| Green Onions | Fresh stem | Comparable to onion | Salads, takeout garnish |
Will a small amount of onion hurt my dog?
Usually not, and it is worth saying that plainly rather than letting every owner assume the worst. For a healthy medium or large dog, a single accidental mouthful of something containing onion, a scrap of burger, a lick of gravy, a piece of pizza with onion on it, generally falls well below the threshold above, and the realistic outcome is nothing or a bout of loose stool.
The situations that change that answer are specific rather than vague. A small dog, where the same absolute amount is a much larger fraction of body weight. A concentrated form, so a teaspoon of seasoning rather than a slice of vegetable. Repeated exposure across several days, because the red-cell damage is cumulative and the recovery is slow. And breed susceptibility: Japanese breeds including the Akita and Shiba Inu have a documented inherited red-cell trait that makes them affected at lower exposures than the general figure suggests.
If your dog is small, is one of those breeds, ate a concentrated form, or has been getting scraps repeatedly, the honest advice is to call rather than to work from a chart. Our checker scales the estimate to your dog's actual weight, and breed and size effects covers why the same meal is a different event in a different dog.
Where the exposure usually comes from
In practice, very few dogs eat a raw onion. They eat things that contain onion, and the label rarely makes that obvious: Gravy, Salsa, Guacamole, Worcestershire Sauce, Steak Sauce, French Onion Dip, Sour Cream and Onion Dip and the whole Allium Seasonings and Mixes shelf.
Bread is a quiet contributor too, because Garlic Bread and Garlic Knots are eaten in quantity and taste like something a dog should be allowed. So are Garlic Mashed Potatoes and anything finished with Garlic Butter.
Peelings, compost and the garden
Onion and garlic skins do not stop being alliums once they are waste. A Compost bin is one of the more reliable routes to a repeated exposure, because the scraps accumulate, the smell is interesting, and nobody is counting what the dog took. If your dog scavenges, the bin is worth securing for this reason alone, along with everything else in what to do if your dog got into the trash.
The garden is a smaller worry than the kitchen but not a zero one. Ornamental alliums, wild garlic and ramps all carry the same compounds, and a dog that digs will find bulbs. Our plant database covers what else is growing out there.
One more thing worth saying plainly: garlic is sold as a natural flea remedy for dogs, and it should not be used that way. The dose that would be needed to deter fleas sits in the same range as the dose that damages red cells, the evidence that it works is poor, and there are effective licensed products. If you are weighing a supplement against a prescription, our medication pages are a better starting point than a health-food aisle.
Signs to watch for
Pale or white gums, weakness, lethargy, reluctance to exercise, rapid or laboured breathing, an elevated heart rate, dark or red-brown urine, jaundice or yellow gums, reduced appetite, vomiting, diarrhoea, drooling and abdominal discomfort.
Check the gums specifically. Lift the lip and look at the colour above the teeth: healthy gums are pink, and pallor is the sign that most reliably distinguishes an allium problem from ordinary stomach upset. Compare with diarrhoea after eating something if the early signs are all gastrointestinal.
What to do next
- Work out what form it was and roughly how much. Fresh, cooked, dried or powdered changes the answer more than the volume does.
- Weigh the amount against your dog's weight using the charts above, or run it through the checker for a weight-specific estimate.
- Call your vet or a poison-control line if the amount is near or above the line, if your dog is small, or if it was a concentrated form.
- Do not rely on your dog seeming fine that evening. The relevant window is the next five days, and pallor or dark urine at any point in it is a same-day call.
- If exposure has been repeated over several days rather than a single meal, say so. Cumulative damage is treated differently from a one-off.
- For a large recent ingestion, go to the first ten minutes rather than monitoring at home.
Available 24/7. A consultation fee may apply.
Frequently asked questions
How much garlic is toxic to dogs?
Around 1 g per kilogram of body weight is the figure most often cited, making garlic several times more potent than onion for the same mass. For a 20 lb dog that is roughly 9 g, or about three supermarket cloves. Published sources vary on the exact multiple, so treat that as approximate and lean conservative when judging a real exposure.
Will a small amount of onion hurt my dog?
For a healthy medium or large dog, a single small accidental exposure usually falls below the threshold and causes nothing worse than loose stool. The situations that change that are a small dog, a concentrated form such as onion powder, repeated exposure over several days, and Japanese breeds like the Akita and Shiba Inu, which have an inherited red-cell susceptibility.
Can dogs eat cooked onions?
Cooking does not remove the risk. Roasting, frying and simmering change flavour and texture but do not break down the organosulfur compounds responsible for the red-cell damage. A dog that ate fried onions off a burger or the onion from a stew has had a real exposure, and it should be judged on the same weight-based threshold as raw onion.
How much shallot is toxic to dogs?
Shallots sit in the same genus and carry the same compounds, so the 0.5%-of-body-weight guidance for onion is the sensible working figure. The practical wrinkle is that shallots usually turn up raw and finely chopped in dressings and pan sauces, which is a more concentrated presentation than a cooked slice, so a smaller volume can matter more than you would expect.
Is onion powder worse than fresh onion?
Per gram, considerably. Drying removes the water and concentrates everything left behind, so a level teaspoon of onion powder stands in for a much larger mass of fresh onion. That is why seasoning blends, soup mixes and dips are a more common route to a meaningful exposure than the vegetable itself, despite looking like a trivial amount.
How long after eating onion will my dog show symptoms?
Typically one to five days, not hours. The damage is done to red blood cells and the resulting anaemia takes time to become apparent, so the absence of signs on the same evening tells you very little. Early vomiting from simple irritation may or may not happen. Watch for pale gums, weakness and dark urine across the following week.
My dog ate onion powder. What should I do?
Work out roughly how much and call your vet or a poison-control line, because powder is the concentrated form and a small measured quantity can carry a meaningful load. Bring the packaging if you have it. Do not wait to see whether signs develop, since the anaemia that matters is delayed by days rather than hours.
Are onions worse for some breeds?
Yes. Japanese breeds including the Akita and Shiba Inu carry an inherited red-cell trait that makes them more susceptible to oxidative damage, so they are affected at lower exposures than the general threshold implies. Body size matters independently: the same absolute amount of onion is a far larger fraction of a small dog's body weight.