Dog Medication Dosage by Weight Calculator
Turn your vet’s mg/kg dose into milligrams, tablets (rounded to halves or quarters) or millilitres for your dog’s weight, with daily and course totals — and compare it with the published reference range for common vet-prescribed dog medicines. Explains why ibuprofen, naproxen and acetaminophen are dangerous for dogs.
How it works
Dose (mg) = weight (kg) × rate (mg/kg) — weight (kg) = weight (lb) × 0.4536 · Daily = dose × doses per day · Tablets = dose ÷ tablet strength, rounded to the nearest piece you can give · Liquid (mL) = dose ÷ concentration (mg/mL) · Reference check: rate and daily mg/kg compared with the published dog range for the chosen medicine · Accidental exposure = tablets × strength ÷ weight (kg), compared with published toxic doses
Almost every animal drug is dosed per kilogram of body weight, so the key step is converting the dog’s weight to kilograms and multiplying by the rate from the label or your vet. Tablets come in fixed strengths, so the calculator divides by the strength and rounds to the whole, half or quarter tablets you can actually give, then shows the dose your dog really gets. If rounding moves the dose by more than 10%, it says so. For a liquid it gives the millilitres to draw up, and for a course it totals the tablets or liquid needed. If you pick a medicine, the calculator shows the published reference range for dogs (oral doses from the Merck Veterinary Manual’s tables) next to your vet’s dose and says whether the prescription falls inside it. A dose outside the range is a reason to ask, not proof of a mistake. Vets adjust doses for the condition being treated, kidney and liver health and other medicines. Human painkillers are treated differently. Ibuprofen, naproxen and acetaminophen get no dose at all: the page shows the doses at which they poison dogs and, if your dog swallowed some, works out the exposure in mg/kg.
Worked example
A 10 kg dog prescribed 5 mg/kg needs 10 × 5 = 50 mg per dose. Given twice daily that is 100 mg per day, and with 25 mg tablets each dose is 50 ÷ 25 = 2 tablets. Suppose instead a 22 lb (9.98 kg) dog is prescribed carprofen at 2.2 mg/kg twice a day: each dose is 9.98 × 2.2 = 22 mg. With 25 mg tablets split in halves the practical dose is 1 tablet (25 mg, 2.5 mg/kg), a 14% rounding change worth checking with the vet. The daily 4.4 mg/kg sits within the published carprofen range. If that same dog swallowed two 200 mg ibuprofen tablets, the exposure is 400 mg ÷ 9.98 kg = 40 mg/kg. That is below the acute kidney-failure range but still a reason to call a vet straight away.
Sources: Merck Veterinary Manual — NSAIDs used for pain management in dogs and cats · Merck Veterinary Manual — Selected analgesics for use in dogs · Merck Veterinary Manual — Antihistamine dosages for integumentary disease · Merck Veterinary Manual — Select therapeutic agents for atopic dermatitis in dogs · Merck Veterinary Manual — Antiulcerative drugs · Merck Veterinary Manual — Antiemetic drugs · Merck Veterinary Manual — Dosages of penicillins / cephalosporins / tetracyclines · Merck Veterinary Manual — Nitroimidazoles (metronidazole) use in animals · Merck Veterinary Manual — Commonly used cardiovascular drugs and dosages · Merck Veterinary Manual — Toxicoses from human analgesics in animals · U.S. FDA — Paws off xylitol; it’s dangerous for dogs
Frequently asked questions
My dog is weighed in pounds — does that matter?
Yes. Doses are written per kilogram, so pounds must be converted first (divide by 2.2046). This calculator does that automatically when you pick the pound unit, but a hand calculation that skips it will overdose the dog by more than double.
Can I round the number of tablets up?
No. Many veterinary drugs — especially NSAIDs, sedatives and heart medications — have a narrow safety window, and rounding up can push the dose into the toxic range. If the math gives an awkward fraction, ask your vet about a different tablet strength or a liquid formulation.
Can I give my dog ibuprofen, naproxen or Tylenol?
No. Ibuprofen and naproxen cause stomach ulcers and kidney failure in dogs at doses close to a human tablet, and acetaminophen (paracetamol) damages the liver and red blood cells. If your dog has swallowed any, call your vet or an animal poison line straight away. For pain, your vet can prescribe a dog-licensed medicine such as carprofen, meloxicam or grapiprant.
Where do the reference ranges come from?
From the dog doses in the Merck Veterinary Manual’s drug tables, by mouth. They are general figures: the right dose for your dog depends on what is being treated, age, kidney and liver function and other medicines, so the dose your vet prescribes takes priority. The calculator only compares, it never replaces a prescription.
Is Benadryl (diphenhydramine) safe for dogs?
Vets do sometimes recommend plain diphenhydramine, typically 2–4 mg/kg every 8–12 hours, but ask yours first. Many human allergy and cold products also contain a decongestant, acetaminophen or xylitol, all dangerous for dogs, and antihistamines are not a treatment for swelling of the face or breathing trouble — those need a vet immediately.
Does this work for cats or other pets?
The mg/kg arithmetic is the same, but cats metabolise many drugs very differently (paracetamol and several NSAIDs are lethal to cats), so never reuse a dog dose for another species. Always get the species-specific rate from a vet.
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Educational estimate only — not veterinary advice. Always consult a licensed veterinarian before dosing, treating, feeding, or making care decisions for any animal.