The Merck Veterinary Manual states that more than one grape or raisin per 4.5 kg, about 10 lb, of body weight may carry enough tartaric acid to risk kidney damage. For a 20 lb dog that is two grapes. Raisins are worse per piece because the water is gone and the acid is concentrated. Individual sensitivity varies enormously, so treat any amount as worth a call rather than working to the line.
The number, by your dog's weight
Merck's stated guidance is the clearest published figure available, and unusually for a toxicology threshold it is expressed as a count of objects rather than a mass: more than one grape or raisin per 4.5 kg of body weight. That works out to roughly 0.22 grapes per kilogram.
The practical readings are startlingly small. A 10 lb dog is at the line on one grape. A 20 lb dog on two. A 60 lb dog on six. If you have just watched a spaniel eat a handful off the floor, that handful is very likely above the stated figure, and the reasonable response is a phone call rather than a wait.
- High risk
- Never
Horizontal: body weight, 5 to 120 lb. Vertical: Number of grapes. Each sloping line is a published threshold, so it sits higher for a heavier dog.
- Above Merck's stated risk guidance — a 20 lb dog reaches this at 2.0 grapes.
View as table
| Dog weight | Reaches Above Merck's stated risk guidance |
|---|---|
| 10 lb | 1.0 grapes |
| 20 lb | 2.0 grapes |
| 30 lb | 3.0 grapes |
| 50 lb | 5.0 grapes |
| 80 lb | 8.0 grapes |
Source: Merck Veterinary Manual
Why this curve is not a permission slip
This page carries a dose curve and an any-amount warning at the same time, and that combination deserves an explanation rather than a shrug, because it looks contradictory.
A threshold exists in the literature and it is worth knowing, because it tells you how urgent a given amount is and it is the figure your vet will be working from. What it does not do is establish a safe dose. The variability in the toxin itself, not the guidance, is what removes that possibility: two grapes from different bunches are not the same exposure, and nobody can tell them apart by looking.
The toxin is tartaric acid, and that is recent news
For decades the honest answer to why grapes hurt dogs was that nobody knew. A great many pages still say exactly that, which is now out of date. The proposed toxic principle is tartaric acid and its potassium salt, identified in 2021, and the Merck Veterinary Manual describes it as the agent responsible.
The mechanism explains why dogs are affected when people are not. Dogs excrete organic acids poorly compared with other species. Tartaric acid accumulates in the cells of the proximal renal tubules, damages them, and the result is acute kidney injury, which can progress to reduced or absent urine production within about 72 hours.
This is the single most useful thing on the page, because it also explains the confusing part. Tartaric acid content varies substantially by grape variety, ripeness and growing conditions. A dog that ate six grapes from one bunch and was fine, and a dog that ate three from another and went into renal failure, are not contradictory anecdotes. They ate different amounts of the actual toxin.
Raisins are worse, piece for piece
A Raisins is a grape with the water removed, and the tartaric acid stays behind. That makes any given raisin a more concentrated dose than any given grape, which is why the same one-per-ten-pounds guidance covers both, and why a handful out of a box is a more serious event than the same handful of fresh fruit.
It is the same principle that makes onion powder more potent than fresh onion, and it is worth learning once because it applies across the pantry. Anything dried is concentrated. The practical result is that Dried Fruit, Trail Mix, Granola, Granola Bars and Breakfast Cereal are the household items that most often deliver a meaningful raisin dose, usually in a quantity nobody measured. Sultanas and currants are the same fruit under different names, which matters if you are reading a British label.
Baked goods deserve a specific mention. A slice of fruit loaf, a hot cross bun, a scone or a Christmas pudding can carry a lot of dried fruit in a form a dog will happily eat fast. Our scenario page on a dog that ate grapes or raisins covers what happens next.
- Never
- High risk
Position along each line shows relative concentration index; the scale runs from 0 to 100.
View as table
| Item | relative concentration index | Tier |
|---|---|---|
| Cream of tartar | 100 | ■ Never |
| Raisins, sultanas | 24 | ■ Never |
| Tamarind | 12 | ◆ High risk |
| Fresh grapes | 6 | ■ Never |
| Grape juice | 5 | ◆ High risk |
Source: Relative index estimated from typical moisture content and composition, shown for scale only. Not a published toxicological measurement; the only sourced threshold on this page is Merck's grape count.
Cream of tartar and play dough
Cream of tartar is potassium bitartrate. It is the same compound family, and it is the reason a batch of homemade play dough is worth taking seriously: many recipes use it in quantity, and the dough is soft, salty and appealing. Our page on Homemade Play-Doh / Salt Dough covers the combination, because those recipes also carry a large salt load, which is a separate and more immediate problem.
Tamarind sits in the same family. It is rarely eaten in quantity by dogs, but it turns up in Worcestershire Sauce, some chutneys and a number of South Asian and Latin American dishes, so it is worth knowing the connection exists. Almost nobody mentions it.
The clock
Grape and raisin toxicosis follows a fairly consistent sequence, and knowing it is what stops an owner being reassured at the wrong moment. Vomiting is usually the first sign and often arrives within six hours, sometimes with pieces of fruit in it. Lethargy and reduced appetite follow. Kidney values begin to rise over the next day, and reduced or absent urine production can develop by around 72 hours.
That timeline is why decontamination is time-sensitive and why a same-day call matters more here than in most exposures. Once kidney injury is established, treatment becomes supportive rather than preventive. How long poisoning symptoms take to show puts this alongside other exposures for comparison.
- High risk
- Never
Hours after the dog ate it, from 0 to 72.
View as table
| What | Signs begin | Through | Tier | Note |
|---|---|---|---|---|
| Vomiting, sometimes with fruit in it | 2 h | 12 h | ◆ High risk | The usual first sign. Easy to write off. |
| Lethargy, off food | 6 h | 36 h | ◆ High risk | Quiet, not himself, not eating. |
| Kidney values rising | 24 h | 72 h | ■ Never | Invisible without bloodwork. This is the diagnosis. |
| Reduced or absent urination | 48 h | 72 h | ■ Never | Established injury. Prognosis worsens sharply here. |
Source: Merck Veterinary Manual
Threshold by weight
| Dog weight | Stated threshold | What to do |
|---|---|---|
| 5 lb | Under 1 grape | Call now. Any amount is at or over the line. |
| 10 lb | 1 grape | Call now. |
| 20 lb | 2 grapes | Call now if it was two or more; call anyway if unsure. |
| 40 lb | 4 grapes | Call. A dropped handful clears this easily. |
| 60 lb | 6 grapes | Call. Count the stems if you can. |
| 80 lb | 8 grapes | Call. Large dogs are not exempt, just further along the line. |
What about other fruit?
The good news is that grapes are the exception rather than the rule, and there is no reason to become frightened of fruit generally. Blueberries, Blackberries, Watermelon, Cantaloupe, Pears and Banana are ordinary treats in sensible amounts, and our safe fruits and vegetables guide covers the portion sizes.
The fruits that need care need it for mechanical rather than chemical reasons: Peaches, Mango and Cherry pits are stone hazards rather than toxins. Grape Juice is the one fruit drink to treat like the fruit itself.
What else is hard on the same kidneys
Grape toxicosis is a kidney event, so anything else straining the same organ at the same time makes it worse. That matters most for dogs already on medication. Ibuprofen and other human anti-inflammatories reduce blood flow through the renal medulla, which is precisely the wrong thing to be happening while tubular cells are being damaged, and it is one more reason never to give a human painkiller to a dog. If your dog is on any prescription, say so when you call.
The bin is the other practical route in. Grape stems, raisin boxes and the dregs of a fruit loaf all end up in the kitchen waste or the Compost bin, and a dog that scavenges is getting a concentrated, uncounted portion. Outdoors, a fruiting grapevine puts the same fruit within reach at dog height for weeks.
For where grapes sit against everything else, the most toxic foods list ranks them alongside the other any-amount items, and the first ten minutes is the page to open if this has just happened.
Signs to watch for
Vomiting, often within a few hours and sometimes containing pieces of grape or raisin, diarrhoea, lethargy, weakness, loss of appetite, abdominal pain or tenderness, increased thirst, and then either an increase in urination or, more ominously, a reduction or complete absence of it. Bad breath with an ammonia-like smell and mouth ulceration can appear as kidney failure progresses.
The one to act on hardest is a change in urination two to three days after a known ingestion. Compare against signs of dog poisoning if you are unsure what you are seeing.
What to do next
- Call your vet or a poison-control line straight away, even if the amount seems trivial and even if your dog is bright and well.
- Count what is missing if you can. Stems, an empty box, the number left in the punnet: all of it helps.
- Do not induce vomiting on your own initiative. Ask first, because whether it helps depends on how long ago it happened: should I induce vomiting.
- Expect bloodwork and, in most cases, a recommendation for intravenous fluids over 48 to 72 hours. How vets treat poisoning explains what that involves.
- If a few days have passed and your dog is drinking more, urinating less, or off food, go in now rather than waiting for it to settle.
- Use the checker for a weight-specific read on the amount.
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Frequently asked questions
Can dogs eat grapes?
No. Grapes and raisins can cause acute kidney injury in dogs, and the Merck Veterinary Manual puts the risk threshold at more than one grape per 4.5 kg of body weight. Because tartaric acid content varies between varieties and growing conditions, some dogs are affected by less, so there is no amount that can be recommended as safe.
How many grapes will hurt a dog?
Merck's stated guidance is more than one grape or raisin per 10 lb of body weight, so two grapes for a 20 lb dog and six for a 60 lb dog. Treat that as the point where published risk begins rather than a safe allowance, since dogs have developed kidney injury on smaller amounts because of variation between bunches.
Why are grapes bad for dogs?
The proposed toxic principle is tartaric acid, identified in 2021. Dogs excrete organic acids poorly compared with other species, so tartaric acid accumulates in the proximal renal tubule cells and damages them, producing acute kidney injury that can progress to reduced or absent urine production within about 72 hours.
Are raisins worse than grapes?
Piece for piece, yes. A raisin is a dried grape, so the water has gone and the tartaric acid is concentrated into a much smaller object. The published guidance counts them the same, one per 10 lb of body weight, which means a handful of raisins is a considerably larger dose than a handful of fresh grapes would be.
My dog ate one grape. Should I worry?
Call your vet or a poison-control line for advice, particularly if your dog is small. One grape is at or above the stated threshold for a dog under 10 lb, and because tartaric acid content varies between grapes there is no reliable way to know whether a single fruit was a low or a high dose. Most vets will want to know.
How long does it take for grape poisoning to show?
Vomiting usually appears within about six hours, often containing pieces of fruit, followed by lethargy and loss of appetite. Kidney values rise over the following day, and reduced or absent urination can develop by around 72 hours. Because the useful treatment window is early, a same-day call matters more than watching for signs.
Is grape juice dangerous to dogs?
Treat it as you would the fruit. Grape juice is pressed from grapes and carries the same tartaric acid, though the concentration depends on the product and whether it is from concentrate. There is no established safe volume, so a dog that has drunk a meaningful amount warrants the same call as one that ate the fruit.
What about cream of tartar and play dough?
Cream of tartar is potassium bitartrate, the same compound family as the tartaric acid in grapes, and many homemade play dough recipes use it in quantity. Those recipes usually carry a large salt load as well, which is a more immediate hazard. A dog that has eaten homemade dough is worth a call for both reasons.