How This Cat Medication Calculator Works
This cat medication calculator is a weight-based dosing math tool. Vets calculate cat doses with one formula: dose (mg) = your cat’s weight (kg) × the prescribed rate (mg/kg), and then volume (mL) = dose (mg) ÷ the liquid’s concentration (mg/mL). This free tool does exactly that arithmetic once you enter the three numbers, and it also converts pounds to kilograms and milligrams to millilitres. What it deliberately does not do is tell you the mg/kg rate for any particular drug — that figure depends on the medicine, the condition being treated and your individual cat’s health, so it has to come from your veterinarian or the pharmacy label. Used that way, the calculator is a safe double-check on the math, not a substitute for a prescription.
For example, if your vet prescribes 5 mg/kg of a liquid that is 50 mg/mL for a 4 kg cat, the dose is 4 × 5 = 20 mg, and the volume is 20 ÷ 50 = 0.4 mL. The tool shows that result along with the working so you can sanity-check the number the pharmacy gave you.
Why You Should Never Guess a Cat’s Dose
Cats are not small dogs, and they are certainly not small people. Their liver processes many drugs slowly, so a dose that is routine for a human or a dog can build up to a toxic level in a cat. The classic example is acetaminophen (paracetamol, Tylenol), which is fatal to cats even in a single tablet, and human NSAIDs like ibuprofen and naproxen, which cause kidney failure at tiny amounts. Dog medicines are risky too — a dog NSAID dose or a dog-strength tablet can seriously harm a cat. This is why veterinary forums and poison lines refuse to give out dosage numbers online: the safe dose genuinely depends on the exact product, the illness and the individual animal.
Use the “Safe for Cats?” tab above before giving any human or dog medicine. If your cat may have swallowed something toxic, treat it as an emergency and call your vet, an emergency animal hospital, or an animal poison control line right away.
Converting Between mg, mL and Weight
Two conversions trip people up most. First, pounds to kilograms: divide the weight in pounds by about 2.2 (exactly 2.2046). A 9 lb cat is roughly 4.1 kg. Second, milligrams to millilitres for a liquid, which needs the concentration printed on the bottle. If the label reads “200 mg / 5 mL”, that is 40 mg/mL, so a 20 mg dose is 0.5 mL. One millilitre (mL) and one cubic centimetre (cc) are the same thing, so a syringe marked in cc works fine.
| What you want |
Formula |
| Weight in kg |
pounds ÷ 2.2046 |
| Total dose (mg) |
weight (kg) × rate (mg/kg) |
| Liquid volume (mL) |
dose (mg) ÷ concentration (mg/mL) |
| Number of tablets |
dose (mg) ÷ tablet strength (mg) |
| mg in a volume |
volume (mL) × concentration (mg/mL) |
About Common Cat Prescriptions
People often search for doses of specific drugs like amoxicillin, Clavamox, azithromycin and doxycycline. These are genuine veterinary antibiotics, but the dose and the number of days vary with the infection, so there is no single “cat dose” to plug in — your vet sets it, and you then use the calculator above only to turn that prescription into mL or tablets. A few practical points worth knowing: human amoxicillin and “fish” antibiotics are not formulated or dosed for cats; doxycycline tablets should always be followed with a little water or food because dry tablets can injure a cat’s throat; and GS-441524, the antiviral used for feline infectious peritonitis (FIP), is not an approved product in most countries and must be supervised by a vet or an established FIP programme — this tool will not calculate a GS dose.
Frequently Asked Questions
How do you calculate a cat’s medication dose?
Use the formula dose (mg) = weight (kg) × rate (mg/kg), then volume (mL) = dose (mg) ÷ concentration (mg/mL). For a 4 kg cat at 5 mg/kg of a 50 mg/mL liquid, that is 20 mg, or 0.4 mL. The mg/kg rate must come from your vet — this calculator does the arithmetic, not the prescribing.
Is it safe to use an online cat dosage calculator?
Only as a math check on a dose your vet has already set. It is not safe to pick a dose yourself from an online tool or a forum, because the right amount depends on the drug, the illness and your cat’s liver and kidney health. Always confirm the final dose with your veterinarian before giving it.
How do I convert my cat’s weight from pounds to kg?
Divide the weight in pounds by 2.2046 (roughly 2.2). So a 9 lb cat is about 4.1 kg and an 11 lb cat is about 5 kg. Cat doses are almost always calculated per kilogram, so this is usually the first step.
How do I turn a dose in mg into mL?
Divide the dose in mg by the liquid’s concentration in mg/mL, which is printed on the bottle. If the label says 200 mg / 5 mL, that is 40 mg/mL, so a 20 mg dose is 0.5 mL. One mL equals one cc.
What human medicines are dangerous for cats?
Acetaminophen (paracetamol, Tylenol) can be fatal to a cat even in one tablet, and human NSAIDs like ibuprofen, naproxen and aspirin cause kidney and stomach damage at tiny doses. Dog NSAIDs and decongestants (pseudoephedrine) are also toxic. Never give a human or dog medicine to a cat without your vet’s say-so.
How much amoxicillin or azithromycin should I give my cat?
There is no single safe number to give here — the dose and duration of antibiotics like amoxicillin, Clavamox, azithromycin or doxycycline depend on the infection and your cat, so your vet must prescribe them. Once you have that prescription, use the Dose & Volume tab to convert it into mL or tablets.
Can I split a cat’s tablet in half?
Sometimes, but not always. Plain scored tablets can usually be halved or quartered, but coated, capsule and extended-release tablets must be given whole. If the math lands on an awkward fraction, ask your vet about a different tablet strength or a liquid rather than guessing.
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PetCalculatorHub Editorial Team
This calculator applies the standard veterinary dosing formula — dose (mg) = body weight (kg) × rate (mg/kg), and volume (mL) = dose (mg) ÷ concentration (mg/mL) — plus pound-to-kilogram (÷ 2.2046) and milligram-to-millilitre conversions. It intentionally contains no drug-specific dose database: the mg/kg rate, dosing frequency and treatment length must come from your prescribing veterinarian, because cats metabolise many drugs differently from people and dogs and a wrong dose can be toxic or fatal. The safety notes on human and dog medicines reflect widely published feline toxicology. This tool is for education and for checking the arithmetic of a dose your vet has already set — it is not veterinary advice and does not replace your veterinarian.
Last updated: October 2026
