The numbers behind it
Chocolate's toxic compounds are methylxanthines — theobromine and caffeine [1][2]. Merck lists their combined content by type [1]:
| Chocolate | Methylxanthines (mg per gram) |
|---|---|
| Cocoa powder | 28.5 |
| Unsweetened baking (baker's) chocolate | 15.5 |
| Semisweet or sweet dark chocolate | 5.6 |
| Milk chocolate | 2.3 |
| White chocolate | 0.04 |
| Cocoa bean hulls (mulch) | 9 |
Dose = grams eaten × mg per gram ÷ dog's weight in kg. Merck reports mild signs (vomiting, diarrhea, thirst) at about 20 mg/kg, heart effects at 40–50 mg/kg and seizures at 60 mg/kg or more [1]. Signs usually start within 6–12 hours [1].
Why we never say “safe, do nothing”
Labels vary, dogs vary, and the fat in chocolate can also trigger pancreatitis [1]. A low estimate is a reason for a calm phone call, not for skipping one.