Benadryl Dosage Calculator for Dogs
Get the vet-standard diphenhydramine dose (2–4 mg/kg, roughly 1 mg per pound) for your dog's exact weight — in milligrams and in tablets — plus the safety checks most dosage charts skip.
Benadryl dosage chart for dogs (by weight)
Based on the standard 1 mg per pound guideline, given every 8–12 hours. Tablet counts assume standard 25 mg tablets.
| Dog weight | Dose per administration | 25 mg tablets |
|---|---|---|
| 5 lb (2.3 kg) | 5 mg | ¼ tablet (ask your vet — small dogs are easiest to overdose) |
| 10 lb (4.5 kg) | 10 mg | ½ tablet |
| 20 lb (9 kg) | 20 mg | ¾–1 tablet |
| 25 lb (11.3 kg) | 25 mg | 1 tablet |
| 50 lb (22.7 kg) | 50 mg | 2 tablets |
| 75 lb (34 kg) | 75 mg | 3 tablets |
| 100 lb (45 kg) | 100 mg | 4 tablets |
What Benadryl is used for in dogs
Vets commonly use diphenhydramine for environmental and seasonal allergies, itching, insect bites and stings, hives, and vaccine reactions. It causes drowsiness in most dogs, which is why some owners use it before travel — though for anxiety and motion sickness, ask your vet about purpose-made options that work better.
Products to never use
Benadryl-D or any "cold & sinus" formula — decongestants (pseudoephedrine, phenylephrine) are toxic to dogs. Liquids with alcohol, and anything containing xylitol — xylitol is severely toxic to dogs even in small amounts. Read the ingredients line every time.
Benadryl for dogs FAQ
How much Benadryl for a 50 lb dog?
About 50 mg — two 25 mg tablets — every 8–12 hours. The acceptable veterinary range for a 50 lb dog is roughly 45–90 mg per dose.
How often can I give it?
Every 8–12 hours (2–3 times daily). Don't exceed 3 doses in 24 hours without veterinary direction.
How long does it take to work?
Usually 30 minutes to an hour. Drowsiness is normal and typically lasts 4–8 hours.
What does an overdose look like?
Agitation instead of drowsiness, racing heart, dilated pupils, dry mouth, tremors or seizures. If you suspect an overdose, call the Pet Poison Helpline (855-764-7661) or an emergency vet immediately.
Can I use Zyrtec or Claritin instead?
Some vets do recommend cetirizine (Zyrtec) or loratadine (Claritin) for dogs — but dosing differs and some formulations (especially "-D" versions) are dangerous. That's a specific ask-your-vet conversation, not a chart lookup.
My dog's face is swelling — should I give Benadryl and wait?
No. Facial swelling, rapidly spreading hives, vomiting after a sting, or any breathing difficulty can precede anaphylaxis. Go to a vet now; call them on the way. Benadryl alone is not a treatment for a severe reaction.
Allergy workups, reactions and ER visits add up fast
Chronic allergies are one of the most common insurance claims for dogs. Accident + illness plans average $62/month — compare real 2026 prices by provider.
Compare pet insurance prices →Related dog calculators
Sources: Merck Veterinary Manual (diphenhydramine, 2–4 mg/kg PO q8–12h); VCA Animal Hospitals; Pet Poison Helpline. Last reviewed August 2026.