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Benadryl Dosage Calculator for Dogs and Cats

Benadryl is a brand of diphenhydramine. The published dose is about 1 mg per pound (2 mg/kg), up to 4 mg/kg for dogs and 3 mg/kg for cats. A 25 lb dog works out to about 25 mg, or one 25 mg tablet. Use only plain diphenhydramine, and ask your vet before giving any medicine.

By Sikander Malik · Updated October 16, 2026 · Sources

Pet

lb

Uses plain diphenhydramine. Dog dose from the Merck Veterinary Manual; cat dose from the AAHA 2023 guidelines (Table 8).

Ask your vet before giving any medicine, and confirm the amount for your pet.

Typical dose (start low)

1× 25 mg tablet

= 25 mg (about 2.2 mg/kg), every 8 to 12 hours, no more than 3 times in 24 hours.

Full range23 mg–45 mg (1–1.5 tablets)
Never exceed45 mg (4 mg/kg) per dose

Only plain diphenhydramine. Never a product with a decongestant (Benadryl-D, or any with pseudoephedrine or phenylephrine). For 12.5 mg children’s products, check the label for xylitol and other active ingredients.

Estimates only, not veterinary advice. Reviewed against the Merck Veterinary Manual antihistamine table and the AAHA 2023 allergic skin disease guidelines, October 2026. Medical disclaimer.

If you think your pet had too much

Call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 (a consultation fee may apply), or go to your nearest emergency vet right away. Do this if you are not sure how much your pet had, or if you see any overdose signs below.

How much Benadryl can I give?

Benadryl is a brand of diphenhydramine, an antihistamine. The published dose is 2 to 4 mg/kg for dogs, every 8 to 12 hours, no more than 3 times in 24 hours (Merck Veterinary Manual), and 2 to 3 mg/kg for cats, every 12 hours (AAHA 2023 guidelines). That works out to roughly 1 mg per pound. The calculator leads with that lower, cautious amount and shows the full range. Always confirm the amount with your vet first, especially for cats and small dogs.

Dog Benadryl doses by weight
Dog diphenhydramine dose by weight
WeightDose per dose25 mg tablets
10 lb9 mg–18 mg0.5 tablet
15 lb14 mg–27 mg1 tablet
20 lb18 mg–36 mg1 tablet
30 lb27 mg–54 mg1.5–2
40 lb36 mg–73 mg1.5–2.5
50 lb45 mg–91 mg2–3.5
60 lb54 mg–109 mg2.5–4
80 lb73 mg–145 mg3–5.5
100 lb91 mg–181 mg4–7
2–4 mg/kg, every 8 to 12 hours, no more than 3 times in 24 hours. Tablet counts are in half steps and never exceed 4 mg/kg. Where no half tablet fits, ask your vet for a liquid or the exact amount.
Source: Merck Veterinary Manual (diphenhydramine 2–4 mg/kg, q8–12h).
Cat Benadryl doses by weight
Cat diphenhydramine dose by weight
WeightDose per dose25 mg tablets
6 lb5 mg–8 mgask your vet
8 lb7 mg–11 mgask your vet
10 lb9 mg–14 mg0.5 tablet
12 lb11 mg–16 mg0.5 tablet
15 lb14 mg–20 mgask your vet
2–3 mg/kg, every 12 hours. Tablet counts are in half steps and never exceed 3 mg/kg. Where no half tablet fits, ask your vet for a liquid or the exact amount.
Source: AAHA 2023 guidelines, Table 8 (diphenhydramine 2–3 mg/kg, q12h).

Check the box: plain diphenhydramine only

Use a product whose only active ingredient is diphenhydramine. Never give a combination product with a decongestant, such as Benadryl-D or anything listing pseudoephedrine or phenylephrine; those can be dangerous for pets. Avoid liquids and children’s formulas that contain xylitol, which is toxic to dogs, unless your vet confirms the product. Read the active ingredient panel every time.

Who should not take it

Talk to your vet before giving diphenhydramine if your pet:

  • is pregnant or nursing;
  • has glaucoma, heart disease or high blood pressure;
  • has an overactive thyroid;
  • has a seizure disorder;
  • has an enlarged prostate or trouble urinating;
  • is already on another sedative or an antidepressant.

From the diphenhydramine precautions in the Merck Veterinary Manual and Plumb’s Veterinary Drug Handbook.

Overdose signs

Too much diphenhydramine can cause:

  • agitation, restlessness or hyperexcitability;
  • a fast heartbeat and dilated pupils;
  • tremors or seizures;
  • heavy drowsiness, dry mouth, or trouble urinating.

If you see any of these, or gave more than the amounts above, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 right away.

Questions owners ask

How much Benadryl can I give my dog?
The Merck Veterinary Manual lists 2 to 4 mg/kg of diphenhydramine for dogs, every 8 to 12 hours, which is roughly 1 mg per pound. A 25 lb dog is about 25 mg (one standard tablet) and a 50 lb dog about 50 mg. Start at the lower end, never exceed 4 mg/kg, and check with your vet first, especially for small dogs.
How much Benadryl can I give my cat?
The AAHA 2023 guidelines list 2 to 3 mg/kg of diphenhydramine for cats, every 12 hours. For many cats that is about half of a 25 mg tablet (12.5 mg), but the window is narrow, so a liquid or a vet-measured amount is often better. Ask your vet before giving a cat any medicine, and never exceed 3 mg/kg.
How often can I give it?
For dogs, every 8 to 12 hours and no more than three times in 24 hours. For cats, every 12 hours. Do not give more often than this, and stop and call your vet if it is not helping or your pet seems unwell.
Can I use Benadryl-D or children’s Benadryl?
No, not Benadryl-D or any product with a decongestant (pseudoephedrine or phenylephrine), which can be dangerous for pets. Children’s liquids and chewables can contain xylitol, which is toxic to dogs. Only use a product whose single active ingredient is diphenhydramine, and check the label every time.
What should I use Benadryl for?
Vets sometimes suggest diphenhydramine for mild itching, a bug bite, or car-sickness. It is not a reliable treatment for anxiety, and it will not fix a serious allergic reaction. For facial swelling, hives, trouble breathing, or any emergency, call your vet or go to an emergency clinic now rather than waiting on an antihistamine.
What if I gave too much?
Call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 (a fee may apply), or go to your nearest emergency vet. Signs of too much include agitation, a racing heart, dilated pupils, tremors or seizures, or heavy drowsiness. Act quickly rather than waiting to see what happens.

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Sources

Estimates only, not veterinary advice. Reviewed against the Merck Veterinary Manual antihistamine table and the AAHA 2023 allergic skin disease guidelines, October 2026. Medical disclaimer.