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For a 30-lb 3-year-old, a common diphenhydramine dose is 12.5 mg (5 mL of 12.5 mg/5 mL) every 6 hours as needed.

Many dogs use diphenhydramine at 1 mg per pound every 8–12 hours, with a veterinarian confirming if it fits your dog.

A typical diphenhydramine dose for many dogs is 1 mg per pound, so a 30-lb dog often lands at 30 mg per dose given every 8–12 hours.

A 16-lb dog often gets 16 mg diphenhydramine per dose, given every 8–12 hours, only with veterinarian approval.

A typical diphenhydramine starting dose for a 40-lb dog is 40 mg per dose, given every 8–12 hours, when a veterinarian says it fits.

A 45-lb dog often lands near a 45 mg diphenhydramine dose per serving, but the safest amount depends on the product and your dog’s health.

An 80-lb dog often lands near 75–100 mg per dose of plain diphenhydramine, spaced 8–12 hours apart, when a vet says it fits the case.

A 90-lb dog’s diphenhydramine amount varies by reason, product strength, and medical history, so a vet should set the exact dose.

Most 10-lb dogs start around 10 mg of diphenhydramine per dose, spaced 8–12 hours apart, after a vet’s OK.

For most 1-year-olds, diphenhydramine isn’t a DIY medicine—get a clinician’s child-specific dose or use another approach.