Antifreeze Toxicity Calculator

The Antifreeze Toxicity Calculator estimates how dangerous a suspected ethylene glycol ingestion is for your dog against the published canine lethal dose.

If You Think Your Dog Swallowed Antifreeze, Act Now

Antifreeze poisoning is one of the few emergencies where minutes genuinely change the outcome. Ethylene glycol is absorbed within a few hours, and the antidote only works while the toxin is still in the bloodstream — before it has been converted into the crystals that destroy the kidneys. Acting quickly does not mean panicking; it means moving through a short list of steps without waiting to see what happens.

1. Phone a vet immediately. Call your own practice, or the nearest emergency clinic if it is out of hours. Say you suspect antifreeze (ethylene glycol) poisoning so they can prepare before you arrive.
2. Note the amount and the time. Work out, as best you can, how much was swallowed and when. If you can, bring the container so the vet can read the exact product and concentration.
3. Use the calculator above for a quick read. Entering your dog's weight, the volume, and the product type gives an immediate sense of how serious the situation is — but the result never replaces the phone call.
4. Do not try to make your dog vomit yourself. Salt, washing soda, and hydrogen peroxide all cause further harm. Whether to empty the stomach is a decision only a vet can make and carry out safely.
5. Do not wait for symptoms. A dog can look almost normal in the first hours and still be in mortal danger. The early window, before signs appear, is exactly when treatment works best.

If the calculator returns any reading other than the "no ethylene glycol" result, treat it as an emergency. The bands exist to convey urgency, not to suggest that a lower number is acceptable. For a broader view of when a sign means a genuine crisis, our guide to recognising a true veterinary emergency covers the warning signs across other situations.

Why Even a Small Amount Is an Emergency

Ethylene glycol is dangerous out of all proportion to how harmless it looks and tastes. It is slightly sweet, which is why dogs drink it willingly, and the dose needed to kill is small. Veterinary toxicology references record a minimum lethal dose of roughly 4.4 to 6.6 millilitres per kilogram of body weight for undiluted ethylene glycol in dogs. For a 10 kg dog, that lower figure is about 44 mL — a few tablespoons. For a small terrier, a few licks from a garage floor can be enough.

This is why the calculator has no "mild" band. With chocolate, a small amount in a large dog can genuinely be a non-event; with ethylene glycol, there is no comparable safe margin. The tool reports the dose your dog swallowed in mL/kg and places it against the lethal threshold:

• No ethylene glycol — the product you selected contains none. This is the only non-emergency result, and it applies to genuine propylene glycol "pet-safe" coolants.
• Moderate (below 1.5 mL/kg) — a clearly dangerous amount. Emergency veterinary care is needed despite the lower number.
• Severe (1.5 to 4.4 mL/kg) — a large dose approaching the lethal range. An immediate emergency.
• Emergency (at or above 4.4 mL/kg) — the amount meets or exceeds the dose recorded as lethal for dogs. Life-threatening.

Every one of those bands above zero recommends the same action: get to a vet now. The difference between them is how little time there may be, not whether to act. The same urgency-first logic drives our chocolate toxicity severity assessment, though chocolate works through an entirely different compound and timeline.

How the Calculator Estimates the Dose

The arithmetic is deliberately simple, because in an emergency a clear estimate beats a precise one that takes too long. The tool multiplies the volume swallowed by the proportion of ethylene glycol in the product, then divides by your dog's weight.

In plain terms: a volume of liquid is only partly ethylene glycol, depending on the product. Concentrated antifreeze is around 95% EG; a pre-mixed 50/50 coolant is about half; a "pet-safe" propylene glycol product contains none. Multiplying the volume by that fraction gives the millilitres of actual ethylene glycol, and dividing by body weight gives the dose in mL/kg that maps to the bands above. Because the product type matters so much, reading the bottle is one of the most useful things you can do before you call — it changes the answer dramatically.

The Three Deceptive Stages of Antifreeze Poisoning

Ethylene glycol poisoning does not progress steadily. It moves through three stages, and the gap between the first and the third is what lulls owners into waiting. Understanding the pattern explains why "he seemed to get better" is such a dangerous reassurance.

The cruelty of this poison is in stage two. A dog that looked drunk in the first few hours can seem steadier by the next morning, and an owner reasonably concludes the worst is over. In reality the ethylene glycol is being converted into oxalate crystals that are already lodging in the kidneys. By stage three the damage is often beyond repair. This is the opposite of how a dog reacts to many other toxins, and it is why a suspected antifreeze ingestion is never a "watch and wait" situation.

Why Ethylene Glycol Destroys the Kidneys

Ethylene glycol itself is only mildly harmful; the danger comes from what the body makes of it. In the liver and kidneys, an enzyme called alcohol dehydrogenase breaks ethylene glycol down through a series of steps, ending in oxalic acid. That oxalic acid binds with calcium in the blood to form calcium oxalate crystals, which accumulate in the kidney tubules and cause acute kidney injury.

The antidote works by jamming that first enzyme. Fomepizole — or ethanol, in clinics that do not stock it — blocks alcohol dehydrogenase so that the ethylene glycol is excreted unchanged instead of being turned into crystals. This is also why timing is everything: once the toxin has already been converted and the crystals have formed, blocking the enzyme can no longer undo the damage. The treatment is a race against the dog's own metabolism, which is something a vet manages with intravenous medication and monitoring, not anything that can be attempted at home. The same principle of species-specific, vet-only treatment applies to safe veterinary medication dosing in general.

Worked Examples

Two worked examples accompany this calculator to show how body weight changes everything. The first follows a 20 kg Labrador that drinks 60 mL of concentrate, producing a dose of 2.85 mL/kg, which the tool reports as severe even though it sits below the lethal figure. The lesson is that "below the lethal dose" is still a same-minute emergency. The second follows a 5 kg Terrier that licks 30 mL of the same product, producing 5.7 mL/kg, past the lethal threshold, from a puddle a large dog might have shrugged off. Together they make the central point: the smaller the dog, the smaller the spill needs to be to become fatal.

Ethylene Glycol Versus Propylene Glycol: Reading the Label

Not every coolant is ethylene glycol, and the difference is enormous. Products marketed as "pet-safe" or "non-toxic" antifreeze usually use propylene glycol instead, which is far less dangerous to dogs — it does not break down into oxalate crystals the same way. Selecting the propylene glycol option in the calculator returns the only non-emergency result, because there is no ethylene glycol to dose.

That said, "less toxic" is not "harmless", and a large volume of any coolant warrants a call to the vet. The bigger risk is misreading the label in a panic. Many ordinary coolants still contain ethylene glycol despite reassuring marketing, so check the active ingredient before you rely on it. If you genuinely cannot tell which product your dog reached, assume ethylene glycol and treat it as an emergency. The same care over labels protects against other sweet-tasting hazards such as the sweetener in our xylitol poisoning risk tool, and the food hazards covered in our guide to other household poisons dangerous to dogs.

Glossary of Key Terms

Ethylene Glycol

The active ingredient in most antifreeze and engine coolant. It is a sweet-tasting alcohol that dogs and cats will drink readily, and its toxicity comes not from the molecule itself but from the breakdown products the body creates from it. The minimum lethal dose in dogs is small — around 4.4 to 6.6 millilitres per kilogram of undiluted product — which is why even a modest spill is a serious hazard.

Calcium Oxalate Crystals

The crystals formed when oxalic acid, a late breakdown product of ethylene glycol, binds with calcium in the blood. These crystals lodge in the kidney tubules and are the direct cause of the acute kidney failure that kills dogs in the final stage of poisoning. Their formation is the reason treatment must begin before the toxin has been fully metabolised.

Fomepizole

The preferred antidote for ethylene glycol poisoning. It blocks alcohol dehydrogenase, the enzyme that converts ethylene glycol into its toxic breakdown products, allowing the unchanged toxin to be excreted safely. It is a prescription treatment given under veterinary supervision, often alongside intravenous fluids, and its effectiveness depends heavily on how soon after ingestion it is started.

Sources and Further Reading

The minimum lethal dose, the staged clinical course, the oxalate mechanism, and the role of fomepizole used in this calculator are drawn from the Merck Veterinary Manual chapter on Ethylene Glycol Toxicosis in Animals and from VCA Animal Hospitals' client guidance on ethylene glycol poisoning in dogs. The dose figures are danger thresholds for emergency assessment, not guidance on any tolerable amount — there is no safe ingestion of ethylene glycol. This page is written for owner triage and does not replace immediate veterinary advice; its clinical content is prepared for review by a practising veterinary surgeon and will be updated if source guidance changes.