About the cat chocolate toxicity calculator
Chocolate is poisonous to cats because it contains theobromine (and a smaller amount of caffeine), stimulant alkaloids that cats metabolize very slowly. What matters is not how many grams a cat ate, but the theobromine dose relative to body weight. This calculator multiplies the amount eaten by the theobromine concentration of that chocolate type, then divides by your cat's weight in kilograms to give a dose in milligrams per kilogram (mg/kg) — the number veterinarians use to judge severity.
The formula
Dose (mg/kg) = amount eaten (g) × theobromine content (mg/g) ÷ body weight (kg). Total theobromine ingested (mg) = amount eaten (g) × theobromine content (mg/g). Pounds are converted to kilograms with 1 lb = 0.45359237 kg before the division.
Theobromine content by chocolate type
- Dry cocoa powder: ~26 mg/g — the most concentrated common form.
- Unsweetened / baking chocolate: ~16 mg/g.
- Dark / semisweet chocolate: ~5.5 mg/g (rises with higher cacao percentage).
- Milk chocolate: ~2 mg/g.
- White chocolate: ~0.009 mg/g — effectively theobromine-free, though its fat and sugar can still upset the stomach.
Dose thresholds used here
These commonly cited theobromine thresholds apply broadly to companion animals: mild signs (vomiting, diarrhea, restlessness, increased thirst) begin near 20 mg/kg; cardiac and neurological effects (elevated heart rate, arrhythmia, tremors) become likely near 40 mg/kg; and doses of 100 mg/kg or more approach the potentially fatal range (the theobromine oral LD50 is roughly 200 mg/kg). Cats are actually less likely than dogs to eat sweet chocolate because they cannot taste sweetness, but they are small, so even a modest bite of dark or baking chocolate can push the dose into the danger zone.
A worked example
A 4 kg cat eats 10 g of baking chocolate (16 mg/g). Total theobromine = 10 × 16 = 160 mg. Dose = 160 ÷ 4 = 40 mg/kg — right at the threshold for serious cardiac signs, so this warrants a call to the vet. To only reach the 20 mg/kg mild threshold, that same cat would need (20 × 4) ÷ 16 = 5 g of baking chocolate.