How Much Benadryl for a 20 lb Dog?
For a 20 lb (9.1 kg) dog, the published veterinary reference range for diphenhydramine is 18.1–36.3 mg every 8–12 hours. Here's what that means in tablets and children's liquid. Confirm the dose with your vet before giving it.
every 8–12 hours · about 20 mg by the "1 mg per lb" rule many vets use
Published veterinary reference range (2–4 mg/kg), not a prescription. Plain diphenhydramine only. Confirm with your vet.
Before you give it
- Plain diphenhydramine only. No "-D", "Sinus", "Cold", "PE" or "PM" products: decongestants and painkillers in them are dangerous for dogs.
- Check liquids and melts for xylitol (birch sugar).
- Call your vet first if your dog has heart disease, glaucoma, high blood pressure, seizures, or is pregnant, a puppy, or on other medicines.
- Swelling of the face or throat, trouble breathing or collapse needs an emergency vet, not a tablet at home.
Benadryl dosage chart for dogs by weight
Reference range 2–4 mg/kg. Tablets rounded to the nearest quarter.
| Dog weight | mg range | 25 mg tablets | Children's liquid (12.5 mg/5 mL) |
|---|---|---|---|
| 5 lb (2.3 kg) | 4.5–9.1 mg | 0.25–0.25 | 1.8–3.6 mL |
| 10 lb (4.5 kg) | 9.1–18.1 mg | 0.5–0.5 | 3.6–7.3 mL |
| 15 lb (6.8 kg) | 13.6–27.2 mg | 0.75–1 | 5.4–10.9 mL |
| 20 lb (9.1 kg) | 18.1–36.3 mg | 0.75–1.25 | 7.3–14.5 mL |
| 25 lb (11.3 kg) | 22.7–45.4 mg | 1–1.75 | 9.1–18.1 mL |
| 30 lb (13.6 kg) | 27.2–54.4 mg | 1.25–2 | 10.9–21.8 mL |
| 40 lb (18.1 kg) | 36.3–72.6 mg | 1.5–2.75 | 14.5–29 mL |
| 50 lb (22.7 kg) | 45.4–90.7 mg | 2–3.5 | 18.1–36.3 mL |
| 60 lb (27.2 kg) | 54.4–108.9 mg | 2.25–4.25 | 21.8–43.5 mL |
| 70 lb (31.8 kg) | 63.5–127 mg | 2.75–5 | 25.4–50.8 mL |
| 80 lb (36.3 kg) | 72.6–145.1 mg | 3–5.75 | 29–58.1 mL |
| 90 lb (40.8 kg) | 81.6–163.3 mg | 3.5–6.5 | 32.7–65.3 mL |
| 100 lb (45.4 kg) | 90.7–181.4 mg | 3.75–7.25 | 36.3–72.6 mL |
Questions owners ask
How many mg of Benadryl can I give a 20 lb dog?
The published veterinary reference range is 2–4 mg per kg. A 20 lb dog weighs about 9.1 kg, so the range is roughly 18.1–36.3 mg every 8–12 hours. Your vet will tell you where in that range to start.
How many 25 mg Benadryl tablets for a 20 lb dog?
About 0.75–1.25 tablets of 25 mg covers the reference range for a 20 lb dog. Only use plain diphenhydramine and confirm with your vet.
How much children's Benadryl liquid for a 20 lb dog?
Children's liquid is usually 12.5 mg per 5 mL, so the range is about 7.3–14.5 mL. Check the label for the strength and for xylitol, which is toxic to dogs.
How often can I give my dog Benadryl?
Every 8–12 hours is the usual interval in veterinary references. If you find you need it for more than a few days, ask your vet about longer-term allergy options.