Important: This calculator is for veterinary professional reference only. Always verify dosages against current formulary references and adjust for individual patient factors. Do not use for self-prescribing.
Select species, enter weight, and choose a medication, then click calculate.
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Introduction
Pet owners and veterinary technicians alike face the same arithmetic challenge every time a compounded medication, oral suspension, or injectable is dispensed: translating a mg/kg dose written on the prescription into the actual milliliters to give a 6.4 kg cat or a 34 kg Labrador. The challenge is greater than it appears. The American Veterinary Medical Association (AVMA) and the Veterinary Drug Handbook (Plumb's) document species-specific pharmacokinetic differences that mean a dose correct for a dog can be toxic for a cat, and a dose correct for a 5 kg cat is proportionally different from one for a 7 kg cat even with the same drug. Compounded medications, which are increasingly common in small animal practice, add another layer: the concentration may differ from the commercial product. This calculator handles the full weight-based pet medication dosage chain for dogs and cats, using the pet's weight in kilograms or pounds, the prescribed dose rate in mg/kg, and the available drug concentration to return the volume to administer in mL. It also flags common cross-species dosing mistakes for the most frequently misused medications.
What This Calculator Does
This calculator computes the dose in mg and volume to administer in mL for weight-based pet medications. Enter the pet's species (dog or cat), weight in kilograms or pounds, the ordered dose rate in mg/kg, and the drug concentration in mg/mL or mg/tablet. The calculator returns the total dose in mg, the volume to administer for liquids, or the number of tablets for solid forms. It includes built-in alerts for the most common species-specific toxicity thresholds for acetaminophen (cats: do not use), aspirin (cats: restricted use), and ibuprofen (dogs and cats: do not use).
The Formula
Weight-based pet medication dosing follows the same arithmetic as human medicine: body weight in kilograms multiplied by the dose rate gives the total dose in milligrams. Dividing by the drug's concentration per mL converts milligrams to a measurable volume. Weight must always be in kilograms; pounds divided by 2.2046 gives kilograms. For tablets, divide the total dose in mg by the tablet strength to get the number of tablets. Partial tablet calculations must account for whether the tablet is scored; many veterinary tablets are not scored and splitting introduces significant dose error.
Step-by-Step Example
Record the pet's current weight in kilograms
Example: Golden Retriever, 32 kg (70.5 lbs). Weigh at each visit; do not use the weight from a previous visit for drug calculations. A 10% weight change over 6 months (e.g., from 32 to 29 kg after illness) represents a proportional change in every weight-based dose. For home administration, owners should use a pet scale or their own scale while holding the pet.
Identify the dose rate from the prescription
Prescription: amoxicillin-clavulanate 13.75 mg/kg twice daily for skin infection. Dose = 13.75 × 32 = 440 mg per dose. Available: amoxicillin-clavulanate 62.5 mg/mL oral suspension. Volume = 440 / 62.5 = 7.04 mL per dose, rounded to 7 mL. Twice daily: 14 mL/day. Course: 10 days. Total required: 140 mL. Standard bottle: 100 mL. A 200 mL bottle or two 100 mL bottles are needed.
Verify drug is safe for the species and at the intended dose
Confirm the drug and dose rate are appropriate for dogs versus cats. Metronidazole, carprofen, and amoxicillin are generally safe for both species at different dose ranges. Acetaminophen: safe for dogs at 10-15 mg/kg, CONTRAINDICATED in cats (hepatotoxic at any dose). Aspirin: safe for dogs at 10-25 mg/kg every 12 hours, used in cats only at 10 mg/kg every 48-72 hours due to slow salicylate metabolism. Ibuprofen: DO NOT USE in dogs or cats.
Calculate and communicate the home dosing instructions
Document: drug name, dose in mg, volume in mL, frequency, route, and course length. For client handout: 'Give 7 mL by mouth twice daily (morning and evening) for 10 days. Shake the bottle well before each dose. Refrigerate and discard any unused medication after 10 days.' Include a dosing syringe marked at the 7 mL line.
Real-World Use Cases
Home Medication Administration After Veterinary Discharge
A 4.5 kg cat is discharged after an upper respiratory infection with doxycycline 5 mg/kg twice daily. Dose = 5 × 4.5 = 22.5 mg per dose. Available: compounded doxycycline 10 mg/mL oral suspension. Volume = 22.5 / 10 = 2.25 mL BID. The owner is instructed to use the 3 mL oral syringe, draw to the 2.25 mL mark, and administer directly into the cheek pouch. The veterinary technician demonstrates the technique and confirms the owner can measure the dose accurately before discharge.
Veterinary Technician Drug Calculation During Clinic Exam
A 9 kg beagle is seen for acute vomiting. The veterinarian orders maropitant (Cerenia) 1 mg/kg subcutaneous once daily for 3 days. Dose = 1 × 9 = 9 mg. Cerenia injection is available at 10 mg/mL. Volume = 9 / 10 = 0.9 mL SC. The technician draws 0.9 mL into a 1 mL syringe, confirms the dose with the veterinarian before administration, and administers the subcutaneous injection in the dorsal neck scruff area. Documents dose, route, and lot number in the patient record.
Pharmacy Compounding Verification
A specialty compounding pharmacy prepares a custom concentration of phenobarbital for a 2.8 kg cat with epilepsy. The prescribing veterinarian orders phenobarbital 2.5 mg/kg twice daily. Dose = 2.5 × 2.8 = 7 mg per dose. The pharmacy compounds phenobarbital 10 mg/mL oral solution in a palatable flavored base. Volume per dose = 7 / 10 = 0.7 mL BID. The pharmacy technician verifies the calculation before the batch is released, confirms the label matches (0.7 mL twice daily), and includes a 1 mL oral syringe with 0.7 mL marked.
Comparison
| Drug | Dog Dose | Cat Dose | Cat Safety Note |
|---|---|---|---|
| Amoxicillin | 10-20 mg/kg BID-TID | 10-20 mg/kg BID | Safe in cats; avoid in penicillin-allergic animals |
| Metronidazole | 10-15 mg/kg BID | 10-15 mg/kg BID | Safe; higher doses cause neurotoxicity in cats |
| Prednisolone | 0.5-2 mg/kg daily | 0.5-2 mg/kg daily | Prednisolone preferred over prednisone in cats (better bioavailability) |
| Carprofen (NSAID) | 2.2 mg/kg BID or 4.4 mg/kg once | NOT APPROVED | Not approved for cats; use meloxicam at low dose under veterinary supervision |
| Acetaminophen | 10-15 mg/kg every 8h (vet-directed) | CONTRAINDICATED | Causes methemoglobinemia and hepatic failure in cats; do not use at any dose |
| Ibuprofen | DO NOT USE | DO NOT USE | Causes GI ulceration and acute kidney injury in both species |
Common Mistakes to Avoid
Using the human OTC dose as a guide for pets. A 200 mg ibuprofen tablet is a standard human dose. In a 5 kg dog, 200 mg equates to 40 mg/kg, which is within the range that causes acute renal failure and GI perforation in dogs. Pet owners who give human OTC pain medications without veterinary instruction are responsible for a significant proportion of pet toxicology emergency calls to the [ASPCA Animal Poison Control Center](https://www.aspca.org/pet-care/animal-poison-control) (888-426-4435). Never administer human OTC medications to pets without specific veterinary authorization.
Confusing prednisolone and prednisone in cats. Prednisone must be converted to prednisolone in the liver before it becomes active. Cats have limited hepatic capacity for this conversion, meaning oral prednisone may produce unpredictable and subtherapeutic plasma levels. Prednisolone achieves consistent bioavailability in cats. Prescriptions for cats should specify prednisolone explicitly, and pharmacy substitution of prednisone for prednisolone in cats is clinically inappropriate even though the two drugs are bioequivalent in humans and dogs.
Splitting non-scored tablets to approximate weight-based doses for small cats. A 5 mg tablet split in half is not reliably 2.5 mg. Studies of tablet splitting show that manual splitting of small, round tablets produces fragments varying from 37% to 63% of the intended dose. For cats under 3 kg requiring fractional tablet doses of drugs like methimazole or prednisolone, request a compounded oral suspension at an appropriate concentration so the dose can be measured precisely in mL.
Frequently Asked Questions
Accuracy and Disclaimer
This calculator provides medication dosage estimates for pets based on user-entered weight and dose rate. Results are for reference only and must be verified against the prescribing veterinarian's written order and the specific drug's current veterinary prescribing information before administration. Species-specific toxicity limits may not be fully captured by this calculator. Never administer any medication to a pet without veterinary authorization. If your pet has ingested a potentially toxic substance, contact your veterinarian or the ASPCA Animal Poison Control Center immediately. This tool does not substitute for professional veterinary medical judgment.
Conclusion
Medication dosage calculations for pets should be performed at every dispensing event, not assumed from memory or "the last time." Compounded medications from specialty pharmacies frequently differ in concentration from batch to batch and from the commercial reference product. Always use the concentration printed on the specific vial or bottle you are dispensing from. For pets requiring anesthetic premedication or procedural sedation, use the Anesthesia Drug Calculator for species-specific anesthetic agent dose ranges. For veterinary fee estimates including medication line items, use the Veterinary Fee Pricing Calculator.
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