Dog Medicine Dosage Calculator

This is a reference estimate, not veterinary advice

Read this first. Everything on this page is a reference estimate based on dose ranges that are widely published for dogs. It is not medical or veterinary advice, and it cannot account for your dog's other medicines, health conditions, allergies, liver or kidney function, or the reason you want to give the medicine at all.

Dose ranges exist because the right number depends on the individual animal. A 40 lb dog with a heart condition and a 40 lb dog with a bee sting may need different handling of the same drug. Only a veterinarian who knows your dog can turn a range into a dose. Use this page to understand the arithmetic and to ask better questions, not to replace the call.

Two rules are absolute. Never give a human medicine that your vet has not approved, and never give a combination product when a single-ingredient one will do. Many human cold and sinus products pair an antihistamine with a decongestant or a pain reliever, and those extra ingredients are the part that hurts dogs. The FDA's Center for Veterinary Medicine covers what is and is not approved for animals.

How weight-based dosing works

Most dog doses are written as milligrams per pound of body weight (mg/lb), sometimes as milligrams per kilogram (mg/kg). Multiply your dog's weight by the rate and you have the dose in milligrams. Then divide by the strength of the tablet or liquid you have, and you have the amount to measure out.

• Dose in mg = body weight in lb x rate in mg/lb
• Tablets = dose in mg / mg per tablet
• Daily total = dose x number of doses per day

Rates are almost always given as a range, and the top of the range is a ceiling, not a target. Vets start low and only move up if the response is inadequate. If you are between two tablet sizes, most vets prefer to round down rather than up, because the therapeutic margin on these drugs is usually comfortable but the side effects are dose-related.

Weight matters more than people expect in small dogs. A 12 lb dog is one third the size of a 40 lb dog, so every milligram counts, and a half-tablet error is a much bigger deal. If you have a small dog and a tablet that needs splitting, ask a pharmacist to split it or use a liquid with a marked dosing syringe. Eyeballing a quarter tablet is how small dogs get overdosed.

Worked example: a 40 lb dog and a 12 lb dog

Diphenhydramine (Benadryl) for a 40 lb dog. The widely cited range is 0.5 to 1.1 mg/lb, and 1 mg/lb is the usual middle value.

• Dose at 1 mg/lb: 40 lb x 1.0 = 40 mg per dose
• Range: 20 mg to 44 mg per dose
• With 25 mg tablets: 40 / 25 = 1.6 tablets per dose
• Every 8 to 12 hours: 2 to 3 doses, so up to 120 mg per day at 3 doses

The same drug for a 12 lb dog. 12 lb x 1.0 = 12 mg per dose, with a range of 6 to 13 mg. Against a 25 mg tablet that is 0.48 of a tablet, so half a tablet is the practical dose. Against a children's liquid at 12.5 mg per 5 mL, 12 mg is 4.8 mL, and the liquid is the better choice here, because half a tablet is easy to get wrong and a syringe is not.

Famotidine (Pepcid AC) for the same 40 lb dog. The usual rate is 0.25 to 0.5 mg/lb every 12 to 24 hours, so 10 to 20 mg per dose. With 20 mg tablets that is half a tablet up to one tablet, twice a day at most. Notice how different the arithmetic feels: same dog, same tablet, completely different answer, because the rate is different. That is why you never carry a dose over from one medicine to another.

Common medicines, rates and tablet strengths

The table below lists the rates this calculator uses. Every number is a published range, and every one of them needs a veterinarian's confirmation for your dog.

Three cautions about this table. First, the prescription rows are listed so you can sanity-check what your vet prescribed, not so you can self-prescribe: the diagnosis and the duration come from your vet. Second, many products are sold as chewables or liquids with different strengths, so check the label rather than assuming. Third, some of these medicines interact with others, diphenhydramine plus a sedative, for example, stacks, and only your vet knows what else your dog is taking. The ASPCA's Animal Poison Control Center is the right call for an exposure.

Human medicines that can kill a dog

The most dangerous thing in this article is not a dose error, it is the wrong drug. A handful of everyday human medicines are severely toxic to dogs at doses a person would take without thinking twice.

• Acetaminophen (Tylenol): damages red blood cells and the liver in dogs. A single regular-strength tablet can seriously harm a small dog.
• Ibuprofen and naproxen (Advil, Aleve): cause stomach ulcers and kidney failure. The margin between a helpful dose and a damaging one is narrow.
• Pseudoephedrine and phenylephrine: the decongestants hidden inside combination cold products raise heart rate and blood pressure and can be fatal.
• Xylitol: a sweetener in sugar-free gum, some peanut butters and some melatonin gummies. It causes a dangerous insulin release and liver failure.
• ADHD stimulants and antidepressants: serious neurological and cardiac effects at human doses.

If your dog has eaten any of these, do not wait for symptoms. Call your veterinarian, an emergency clinic or an animal poison control hotline immediately and have the package in front of you so you can read the strength and the amount. Treatment is far more effective early, and "wait and see" is the choice that turns a recoverable exposure into a fatal one.

How to measure and give a dose safely

Once you have a number, the practical part is getting that number into the dog. Four habits prevent most accidents.

Weigh the dog, do not guess. A 40 lb estimate can easily be a 46 lb dog, and 15% matters. A bathroom scale works: weigh yourself holding the dog, then weigh yourself alone, and subtract.

Use the right measuring tool. For tablets, a pill splitter is more accurate than a knife. For liquids, use the dosing syringe that came with the product or a marked oral syringe, a kitchen spoon is roughly a teaspoon and can be off by 20% or more. For small doses, ask a compounding pharmacy to make the strength you need instead of splitting a big tablet into eighths.

Hide it properly. Pill pockets, peanut butter (check for xylitol), cheese or a small piece of hot dog all work. Give the medicine before the meal if the drug is supposed to be taken on an empty stomach, and check the label: famotidine can be given with or without food, while some other drugs cannot.

Write down what you gave and when. The single most common dosing mistake is a second dose given because the first was forgotten, or because a second person in the house gave it. Keep a note on the fridge with the time of each dose. If a dose is missed and you are not sure what to do, call your vet rather than doubling up.

What this calculator cannot know

Four things sit outside any dose calculator, and they are the reason a veterinarian still has to be involved.

Why you are dosing. Itching, a bee sting, motion sickness and anxiety can all be treated with diphenhydramine, but the same symptom can also be a sign of something that needs a different drug entirely. Treating the symptom can hide the problem.

What else your dog takes. Sedatives, opioids, some antibiotics and seizure medicines can interact with antihistamines and antacids. A dose that is safe alone can be too much in combination.

Health conditions. Liver and kidney disease change how fast a drug clears. Glaucoma, heart disease, diabetes, pregnancy and thyroid conditions all shift what is acceptable. Puppies and seniors metabolise differently from a healthy adult dog.

Species and breed. Collies and related herding breeds carry a mutation that changes how some drugs behave. Cats are not small dogs, and several medicines that are fine for a dog are toxic to a cat in the same household. If you have both, keep the pills separate and labelled.

Bottom line: use the numbers here to understand the size of a dose and to check what your vet prescribed. Then make the decision with your vet. This page is a reference estimate and is not medical or veterinary advice.