How the dose is calculated
Chocolate is poisonous to dogs because of two related chemicals, theobromine and caffeine, together called methylxanthines. The calculator multiplies the weight of chocolate eaten by the methylxanthine content of that type of chocolate to get the total, then divides by your dog's weight to give a dose in milligrams per kilogram (mg/kg).
The Merck Veterinary Manual gives the content as 28.5 mg per gram for cocoa powder, 15.5 for unsweetened baking chocolate, 5.3 to 5.6 for semisweet and dark chocolate, 2.3 for milk chocolate and 0.04 for white chocolate. Cocoa bean hulls, sold as garden mulch, are 9 mg per gram. For dark chocolate this page uses 5.6, the top of the range, so the dose is not understated.
The page works in kg and grams and converts exactly, without rounding the amount first.
What the dose means
The Merck Veterinary Manual lists these effects in dogs: mild signs such as vomiting, diarrhoea and increased thirst from 20 mg/kg; heart effects at 40 to 50 mg/kg; seizures at 60 mg/kg or more; and an oral LD50 (the dose that kills half of the dogs tested) of 100 to 200 mg/kg. It adds that severe signs and death can occur at lower doses and that individual dogs differ. The calculator shows which band your dose falls in, but a dose under 20 mg/kg is not a guarantee of safety.
Signs usually begin 6 to 12 hours after eating according to Merck; PDSA says they usually appear within two to four hours but can take up to 12. Do not wait for signs before you call.
Worked example: 10 kg dog, 100 g milk chocolate
For a 10 kg dog that has eaten 100 g of milk chocolate, the dose is 23.0 mg/kg (230 mg of methylxanthines in total). That is in the mild-signs band, which starts at 20 mg/kg, and the amount that would just reach 20 mg/kg is 87.0 g.
The same 10 kg dog eating the same amount of plain or dark chocolate gets 56.0 mg/kg, in the heart-effects band, because dark chocolate carries more than twice as much as milk chocolate per gram.
Size matters
A bigger dog gets a smaller dose from the same chocolate. The same 100 g of plain or dark chocolate gives a 25 kg dog 22.4 mg/kg, in the mild-signs band, compared with 56.0 mg/kg for a 10 kg dog.
White chocolate
Merck calls white chocolate a negligible source of methylxanthines: 100 g eaten by a 10 kg dog is 0.4 mg/kg. PDSA points out that the fat and sugar in it can still upset the stomach and, in severe cases, cause pancreatitis, so ring your vet if your dog has eaten a lot.
What to do now
Ring your own vet or an out-of-hours vet immediately, even if your dog seems well. PDSA advises calling straight away and keeping the packaging, and not trying to make your dog sick at home. If it is quicker, the Animal PoisonLine, run by the Veterinary Poisons Information Service, takes calls on 01202 509 000 at any time; it charges £35 to £45 per call (£35 from 8am to 8pm, Monday to Friday, and £45 at all other times). Tell them your dog's weight, what chocolate was eaten, how much, and when.
What this calculator leaves out
It covers dogs only, and only the six types listed. It does not cover cats, coffee, cocoa beans or instant cocoa, because the figures for them were not available to us from a source we could read. The content of real chocolate varies by brand and cocoa percentage: a bar of 85% dark chocolate can be stronger than the average used here, so treat the dose as a minimum estimate for strong dark chocolate. Many chocolate products also contain raisins, macadamia nuts or the sweetener xylitol, which are separate dangers that this calculator does not measure.
This calculator is not veterinary advice. It is a guide to help you describe the situation to a vet or a poison helpline, not a reason to wait.
Other versions of this calculator
Choosing another country above the inputs opens its own page and resets the inputs.
For US units and wording, open the US dog chocolate calculator.
To plan your dog's food, use the UK dog raw diet calculator.
Inputs for the UK dog chocolate calculator
Type of chocolate
Choose the closest match. Dark chocolate with a high cocoa content can be stronger than the figure used.
Your dog's weight
Current weight in kilograms.
Amount of chocolate eaten
The weight of the chocolate eaten, in grams, not the weight of the packet. Estimate high if unsure.
CALCULATOR QUESTIONS
UK dog chocolate calculator questions
How much chocolate is toxic to a dog?
It depends on the chocolate and your dog's weight. The Merck Veterinary Manual lists mild signs from 20 mg/kg of methylxanthines. For a 10 kg dog that is 87.0 g of milk chocolate.
My dog ate chocolate. What should I do?
Contact your vet, an out-of-hours or emergency vet, or a poison helpline straight away, keep the packaging, and do not wait for signs. Do not try to make your dog sick at home.
Is dark chocolate worse than milk chocolate?
Yes. Merck lists 5.3 to 5.6 mg per gram for semisweet and dark chocolate and 2.3 for milk chocolate, so the same amount of dark chocolate gives a dose more than twice as large.
Is white chocolate safe for dogs?
It contains almost none of the poisonous chemicals, 0.04 mg per gram, but the fat and sugar can still upset your dog's stomach. Ring your vet if a lot was eaten.
How long until my dog shows signs?
Merck says signs usually begin 6 to 12 hours after eating. PDSA says they usually appear within two to four hours but can take up to 12. Do not wait for them before calling.
Does a low dose mean my dog is safe?
Not necessarily. The thresholds are guides; Merck notes that severe signs can occur at lower doses and that dogs differ. Always check with a vet.