Cat Benadryl Dosage Calculator

Estimate a cat's Benadryl (diphenhydramine) dose from body weight using the standard 1 mg per pound guideline, given every 8–12 hours. Always confirm with your vet.

Quick Facts

Method
Diphenhydramine at 1 mg per lb of body weight (≈2.2 mg/kg) per dose
Given every 8–12 hours, up to 3 times daily. Confirm with your veterinarian.

Your Results

Calculated
Dose per administration
-
Diphenhydramine at 1 mg/lb
Standard 25 mg tablets
-
Per dose (fraction of a tablet)
Children's liquid
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12.5 mg / 5 mL (2.5 mg/mL)
Max per day
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3 doses, every 8 hours

Ready

Enter your cat's weight and calculate the dose.

How the cat Benadryl dose is calculated

Benadryl is the brand name for diphenhydramine, a first-generation antihistamine. Veterinarians dose it by body weight. The widely used guideline is 1 mg of diphenhydramine per pound of body weight — equivalently about 2.2 mg per kilogram — per dose, given every 8 to 12 hours (up to three times a day). The arithmetic is simply:

Dose (mg) = body weight (lb) × 1 mg/lb

For a cat weighed in kilograms, convert first (1 kg = 2.205 lb) or multiply the kilogram weight by 2.2 directly. Because most house cats weigh 6–15 lb, typical single doses land between about 6 mg and 15 mg — well under a single 25 mg tablet.

Important: this calculator is an educational estimate, not a prescription. Diphenhydramine is not FDA-approved for cats, and cats can be sensitive to it. Always confirm the dose, frequency, and whether Benadryl is appropriate at all with your veterinarian before giving it.

Why cats are dosed by weight

Antihistamines distribute through the body roughly in proportion to body mass, so a 5 lb kitten and a 15 lb cat need very different amounts. Dosing by weight keeps the concentration in the bloodstream in the effective-but-safe range. Under-dosing does little; over-dosing risks sedation, agitation, rapid heart rate, dry mouth, urine retention, and in large overdoses, seizures.

Turning milligrams into tablets or liquid

Once you know the milligram dose, you have to measure it out from a real product:

  • 25 mg tablets (standard adult Benadryl): a 10 lb cat's 10 mg dose is 10 ÷ 25 = 0.4 of a tablet. Quartering a tablet is imprecise, so tablets suit only larger cats whose dose is close to a clean fraction.
  • Children's liquid (12.5 mg per 5 mL, i.e. 2.5 mg/mL): a 10 mg dose is 10 ÷ 2.5 = 4 mL, measured with an oral syringe. Liquid is usually the most accurate option for cats. Confirm the label lists diphenhydramine as the only active ingredient and contains no xylitol, alcohol, or decongestant.

Common reference doses

  • 5 lb (2.3 kg) cat → ~5 mg per dose (2 mL liquid, 0.2 tablet)
  • 8 lb (3.6 kg) cat → ~8 mg per dose (3.2 mL liquid, 0.32 tablet)
  • 10 lb (4.5 kg) cat → ~10 mg per dose (4 mL liquid, 0.4 tablet)
  • 12 lb (5.4 kg) cat → ~12 mg per dose (4.8 mL liquid, 0.48 tablet)
  • 15 lb (6.8 kg) cat → ~15 mg per dose (6 mL liquid, 0.6 tablet)

Frequently Asked Questions

How much Benadryl can I give my cat?
The standard guideline is about 1 mg of diphenhydramine per pound of body weight (≈2.2 mg/kg) per dose, every 8–12 hours. A 10 lb cat gets roughly 10 mg per dose. This is an estimate — confirm with your veterinarian, because Benadryl is not officially approved for cats and some cats should not take it.
Can I use adult 25 mg tablets, or should I use liquid?
Both contain diphenhydramine, but a cat's dose is usually a small fraction of a 25 mg tablet, which is hard to split accurately. Children's liquid at 12.5 mg per 5 mL (2.5 mg/mL) lets you draw up small, precise volumes with an oral syringe, so it is often the better choice for cats. Never use "Benadryl-D" or any product with added decongestants (pseudoephedrine/phenylephrine) or xylitol — those are dangerous to cats.
How often can I give it, and when should I avoid it?
Every 8–12 hours, up to three doses in 24 hours. Avoid Benadryl in kittens under 6 months, pregnant or nursing cats, and cats with heart disease, high blood pressure, glaucoma, an enlarged prostate, hyperthyroidism, or those on other medications, unless your vet directs otherwise. Watch for excessive sedation or, paradoxically, hyperexcitability.
What are the signs of a Benadryl overdose in cats?
Overdose signs include extreme drowsiness or, conversely, agitation and restlessness, a racing heart, dilated pupils, dry mouth, difficulty urinating, tremors, and in severe cases seizures. If you suspect an overdose, contact your veterinarian or an animal poison control hotline immediately.

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