🐱 Feline Drug Dose Calculator 😺
Precision dosing for cats · mg/kg, BSA, allometric scaling · with full step‑by‑step tutor
📊 BSA: cat vs other species
📈 Dose curve (0.5–12 kg)
🐈 Feline drug dosing – a comprehensive 1500+ word guide
Cats are not small dogs – they have unique metabolism, deficient glucuronidation, and high sensitivity to many drugs. This calculator incorporates feline-specific BSA constants, allometric scaling, and over 30 drug examples.
1. Why cats are different
Cats have low activity of UDP‑glucuronosyltransferase, meaning they metabolise drugs like paracetamol, aspirin and NSAIDs much slower. A seemingly safe canine dose can be fatal. Always use feline‑adjusted doses. Weight alone is insufficient – body condition, age and breed matter. Our calculator uses multiple methods.
2. Body Surface Area (BSA) in cats
The most accurate BSA formula for cats: BSA (m²) = 0.1 × (kg)^0.6667. Derived from multiple allometric studies. BSA is vital for chemotherapy, hormone therapy and some critical care drugs. For a 4.5 kg cat: BSA = 0.1 × 4.5^0.6667 = 0.1 × 2.74 ≈ 0.274 m².
3. Commonly used drug classes in cats
4. Allometric scaling – the ¾ power rule
Dose = reference dose × (BW / refBW)^0.75. If a 10 kg dog needs 100 mg, a 4.5 kg cat would need 100 × (4.5/10)^0.75 = 100 × 0.55 = 55 mg (12.2 mg/kg) – often safer than linear scaling. The calculator shows both.
5. Feline BSA constant and comparison
Our feline constant k = 0.1 is based on the formula: BSA = k × (weight in g)^(2/3) / 10,000. For cats the average k = 10.0 (when using grams). Converted to kg: 0.1. This matches values used in veterinary oncology.
6. Step‑by‑step example
Take a 4.2 kg cat needing amoxicillin at 15 mg/kg, concentration 50 mg/mL. Step 1: weight 4.2 kg. Step 2: dose = 4.2 × 15 = 63 mg. Step 3: volume = 63 / 50 = 1.26 mL. Step 4: BSA = 0.1 × 4.2^0.6667 = 0.1 × 2.62 = 0.262 m². If using BSA method (200 mg/m²): dose = 0.262 × 200 = 52.4 mg. The calculator shows both routes.
7. Geriatric, paediatric and obese cats
For kittens (< 6 months) liver enzymes immature – consider 30% lower dose. Geriatric cats (>12 years) often have reduced renal clearance – use lower end (0.7x protocol). Obese cats: dose should be based on ideal weight + 30% adjustment, not actual weight – our low‑dose protocol mimics this.
8. Toxic drugs in cats – absolute contraindications
Paracetamol (acetaminophen) – causes methemoglobinemia, fatal even at low doses. Aspirin – extremely long half‑life (40 h), use only with caution. Essential oils (tea tree, wintergreen) – neurotoxic. Permethrin (dog spot‑on) – deadly. Always verify with a veterinarian.
9. Drug administration and monitoring
Cats are masters at hiding illness. After administering a drug, observe for appetite, vomiting, lethargy. Therapeutic drug monitoring (e.g., phenobarbital) recommended. Our PDF report helps document the calculation for the clinical record.
10. Oral vs injectable – volume limits
Maximum IM injection site in cats: 1–2 mL per site. Subcutaneous: up to 10–20 mL depending on size, but divided. Oral liquids: max 3–5 mL per administration – our volume display helps avoid overfilling syringes.
11. Compounding and transdermal gels
Many feline drugs are compounded into fish‑flavoured suspensions or transdermal gels. Absorption varies – the calculator dose is for oral/Injectable. Transdermal may need 1.5× dose – discuss with your vet.
12. Breed variations
Siamese, Bengal and Sphynx may have faster metabolism due to higher cardiac output. Persian and Exotic shorthair may have slower clearance. Maine Coon large size needs higher absolute dose, but per‑kg may be slightly lower. Our breed selector adjusts BSA constant slightly (Siamese +5%, Persian –5%).
13. How to use the charts
The BSA chart compares your cat's BSA with dog, horse, human – to visualise why cats need lower doses. The dose curve shows how required dose changes from 0.5 kg kitten to 12 kg giant cat.
14. PDF report – veterinary communication
Click “PDF report” to generate a professional summary including all steps, BSA, dose, volume, and drug class. Perfect for attaching to patient files or emailing to colleagues.
15. References and further reading
Plumb’s Veterinary Drug Handbook (9th ed), The Merck Veterinary Manual, British Small Animal Veterinary Association (BSAVA) Formulary, Journal of Feline Medicine and Surgery (2020–2025).
16. Emergency drugs – quick reference
Atropine 0.02–0.04 mg/kg IV; Epinephrine 0.01 mg/kg IV; Dexamethasone 0.5–2 mg/kg; Diphenhydramine 1–2 mg/kg IM (for allergic reactions).
17. Kidney disease and dose adjustment
In CKD (stage 2–3), drugs excreted renally (e.g., amoxicillin, enrofloxacin) need extended intervals or lower dose. Our “geriatric” protocol can be used as a proxy for 25% reduction.
18. Liver disease and dose adjustment
In hepatic insufficiency, drugs like diazepam, phenobarbital, NSAIDs require ≥50% reduction. Always choose lowest effective dose – calculator’s low‑dose protocol approximates this.
19. Chemotherapy in cats – BSA mandatory
Doxorubicin, cyclophosphamide, lomustine – dose in mg/m². Our BSA method uses the correct feline constant 0.1. Example: 4 kg cat → BSA = 0.1 × 4^0.6667 = 0.1 × 2.52 = 0.252 m². For doxorubicin 25 mg/m², dose = 6.3 mg. Vital accuracy.
20. Final disclaimer
This tool is for educational purposes and clinical support – it does not replace professional veterinary judgment. Always consult a veterinarian before administering any medication. The authors assume no liability for adverse events.
© 2026 Feline Pharmacology Project – dedicated to healthier, happier cats.
🐱 Feline dosing formulas – complete reference
🐈 1. Feline Body Surface Area
BSA = 0.1 × W0.6667 (m²)
Derived from: BSA (cm²) = 10 × (W in g)2/3 / 10000
⚖️ 2. Weight‑based dose
Dose (mg) = W × dose rate (mg/kg)
Example: 4.5 kg × 10 mg/kg = 45 mg
📏 3. BSA‑based dose
Dose (mg) = BSA × dose rate (mg/m²)
Example: 0.274 m² × 200 mg/m² = 54.8 mg
📈 4. Allometric (metabolic) dose
Dose = reference total × (W / Wref)0.75
If a 10 kg dog needs 200 mg, a 4 kg cat: 200 × (4/10)0.75 = 200 × 0.5 = 100 mg
💧 5. Volume to administer
Volume (mL) = Dose (mg) ÷ Concentration (mg/mL)
Breed‑specific k‑factors
Cat Drug Dose Calculator – Getting the Medicine Right for Your Feline Friend
It's late on a Sunday night. Your cat is sick—maybe vomiting, maybe listless, maybe just not acting like themselves. You still have some antibiotics left over from their last infection, and you're tempted to give a little. Or maybe the vet prescribed a medication but the dose on the bottle seems confusing. How much should you really give? A little more for a bigger cat? A little less if they're small?
This is the moment when every cat owner faces a terrifying reality: giving the wrong amount of medication to a cat can be dangerous, even fatal. Cats aren't small dogs. Their bodies process drugs differently, and the margin for error is much smaller than you might think.
A Cat Drug Dose Calculator takes the guesswork out of this nerve-wracking situation. It helps ensure your feline friend gets exactly the right amount of medication based on their weight, the drug, and the condition being treated.
Why Cats Are Different
Before we dive into calculators, let's talk about why cat dosing is so tricky. Cats have unique metabolisms that make them different from dogs, humans, and most other mammals.
Liver metabolism: Cats are deficient in certain liver enzymes that help break down drugs. This means many medications stay in their systems longer and can reach toxic levels more easily. Drugs that are perfectly safe for dogs can kill cats .
Kidney function: Cats evolved from desert ancestors and have highly concentrated urine. This affects how drugs are eliminated and can lead to accumulation of certain medications .
Size variation: A small cat might weigh only 2.5 kg (5.5 pounds), while a large tomcat could be 7 kg (15 pounds) or more. That's a huge range, and dosing by "half a pill" doesn't account for it .
Hiding illness: Cats are masters at concealing symptoms. By the time you notice something wrong, they may be sicker than they appear, which affects how they'll handle medication .
These factors mean that precise dosing isn't just important—it's essential.
When You Need a Cat Drug Dose Calculator
A good calculator helps in several common situations:
- Prescription medications: Your vet prescribes a drug and gives a dose range based on weight. You need to calculate the exact amount for your cat.
- Over-the-counter medications: Sometimes vets recommend OTC drugs like Benadryl or Pepcid for cats. The doses aren't on the box—you need to calculate them .
- Liquid medications: Converting mg/kg doses to milliliters of liquid suspension confuses many pet owners.
- Compounded medications: If your cat needs a custom formulation, you need accurate dose calculations.
- Emergency situations: When you can't reach your vet immediately, having a reliable way to calculate doses can be critical .
The Basic Formula
Most veterinary drug doses are prescribed in milligrams per kilogram of body weight (mg/kg). The basic formula is simple:
Dose (mg) = Cat's weight (kg) × Recommended dose (mg/kg)
But then you often need to convert that to milliliters of liquid medication or fraction of a tablet. That's where step-by-step calculations become essential.
Let's walk through some common scenarios.
Scenario 1: Liquid Medication Calculation
The situation: Your vet prescribes amoxicillin for your cat's infection. The dose is 10 mg/kg twice daily. Your cat weighs 4.5 kg. The medication comes as a liquid suspension with a concentration of 50 mg/mL. How many milliliters do you give each time?
Step 1: Calculate the total dose in milligrams.
4.5 kg × 10 mg/kg = 45 mg
Step 2: Convert milligrams to milliliters using the concentration.
Concentration = 50 mg/mL
Milliliters needed = 45 mg ÷ 50 mg/mL = 0.9 mL
Step 3: Check if this seems reasonable. For most oral syringes, 0.9 mL is easy to measure accurately.
Step 4: The calculator might note: "Draw up 0.9 mL in the oral syringe. Give this amount twice daily, approximately 12 hours apart."
Final answer: Give 0.9 mL of the suspension each time.
Scenario 2: Tablet Fraction Calculation
The situation: Your vet prescribes prednisolone for your cat's inflammatory condition. The dose is 1 mg/kg once daily. Your cat weighs 3.2 kg. You have 5 mg tablets. What part of a tablet should you give?
Step 1: Calculate the total dose in milligrams.
3.2 kg × 1 mg/kg = 3.2 mg
Step 2: Determine what fraction of a 5 mg tablet this represents.
3.2 mg ÷ 5 mg = 0.64 of a tablet
Step 3: Convert to a practical measurement. 0.64 is roughly ⅔ of a tablet. Some pill splitters can cut tablets into halves or quarters, but thirds are tricky.
Step 4: The calculator might offer alternatives: "Since 0.64 of a tablet is difficult to measure accurately, consider asking your vet about a liquid formulation or a different tablet strength. If you must use these tablets, the closest practical dose would be ½ tablet (2.5 mg) or ¾ tablet (3.75 mg). Consult your vet before adjusting."
Final answer: The precise dose is 0.64 of a tablet, but this is impractical. Contact your vet for guidance on accurate dosing.
Scenario 3: Multiple Cats, Different Weights
The situation: You have three cats who all need the same deworming medication. The dose is 5 mg/kg once. Cat A weighs 3.8 kg, Cat B weighs 5.2 kg, Cat C weighs 2.9 kg. The medication is a paste with concentration 10 mg per 0.1 mL (which is 100 mg/mL). Calculate each dose.
Step 1: Calculate milligrams for each cat.
- Cat A: 3.8 kg × 5 mg/kg = 19 mg
- Cat B: 5.2 kg × 5 mg/kg = 26 mg
- Cat C: 2.9 kg × 5 mg/kg = 14.5 mg
Step 2: Convert to milliliters using concentration 100 mg/mL.
- Cat A: 19 mg ÷ 100 mg/mL = 0.19 mL
- Cat B: 26 mg ÷ 100 mg/mL = 0.26 mL
- Cat C: 14.5 mg ÷ 100 mg/mL = 0.145 mL
Step 3: Convert to convenient syringe measurements. Most syringes have markings at 0.01 mL increments.
- Cat A: 0.19 mL (draw to the 0.19 mark)
- Cat B: 0.26 mL (draw to the 0.26 mark)
- Cat C: 0.15 mL (rounding 0.145 to 0.15 is acceptable for most medications, but check with your vet)
Final answer: The calculator provides each cat's specific dose and reminds you to use a separate syringe for each cat to avoid cross-contamination.
Scenario 4: Calculating Duration of Treatment
The situation: Your vet prescribes a 14-day course of antibiotics. The dose is 8 mg/kg twice daily. Your cat weighs 4.2 kg. The bottle contains 50 mL of suspension with concentration 40 mg/mL. Do you have enough for the full course?
Step 1: Calculate each dose in mg.
4.2 kg × 8 mg/kg = 33.6 mg per dose
Step 2: Convert to mL per dose.
33.6 mg ÷ 40 mg/mL = 0.84 mL per dose
Step 3: Calculate daily volume.
Two doses per day = 0.84 mL × 2 = 1.68 mL per day
Step 4: Calculate total volume for 14 days.
1.68 mL/day × 14 days = 23.52 mL
Step 5: Compare to bottle size. The bottle contains 50 mL, which is more than 23.52 mL.
Final answer: Yes, you have enough medication. You'll use about 23.5 mL of the 50 mL bottle, leaving extra in case of spills or missed doses.
Critical Safety Considerations
A Cat Drug Dose Calculator is a tool, not a substitute for veterinary advice. Here are the non-negotiables:
Never use human medications without veterinary approval. Many human drugs are toxic to cats. Acetaminophen (Tylenol) can kill a cat with just one tablet. Ibuprofen causes kidney failure. Even seemingly harmless medications can be dangerous .
Never use dog medications on cats. Permethrin, found in many dog flea treatments, is highly toxic to cats. Other drugs have different safe dose ranges between species .
Always verify concentrations. Liquid medications come in different strengths. Using the wrong concentration can lead to a tenfold dosing error. Check the label carefully.
When in doubt, ask your vet. A quick phone call can prevent a tragedy. Most veterinary clinics are happy to answer dosing questions .
Monitor for side effects. Even correct doses can cause reactions in some cats. Watch for vomiting, diarrhea, lethargy, or behavior changes after starting a new medication .
Reference Table: Common Cat Medications and Typical Doses
| Medication | Typical Use | Typical Dose (mg/kg) | Notes |
|---|---|---|---|
| Amoxicillin | Bacterial infections | 10-20 mg/kg twice daily | Broad-spectrum antibiotic |
| Clavamox | Bacterial infections | 12.5-25 mg/kg twice daily | Amoxicillin with clavulanate |
| Metronidazole | Diarrhea, certain infections | 10-25 mg/kg once or twice daily | Bitter taste, may need compounding |
| Prednisolone | Inflammation, allergies | 1-2 mg/kg once or twice daily | Always taper off, don't stop abruptly |
| Meloxicam | Pain, inflammation | 0.05 mg/kg once daily (short term only) | Cat-specific formulation required |
| Benadryl (diphenhydramine) | Allergies, mild sedation | 1-2 mg/kg twice daily | Use dye-free formulations only |
| Pepcid (famotidine) | Acid reflux, stomach issues | 0.5 mg/kg once or twice daily | Often used for kidney disease nausea |
| Cerenia (maropitant) | Vomiting, nausea | 1 mg/kg once daily | Prescription only, very effective |
Note: These are general ranges only. Always follow your veterinarian's specific prescription.
Factors That Can Affect Dosing
Weight-based dosing is the starting point, but other factors can influence the right dose for your cat:
Age: Kittens and senior cats may process drugs differently. Very young kittens have immature livers and kidneys. Senior cats may have reduced organ function that affects drug clearance .
Kidney or liver disease: Cats with compromised kidneys or livers need lower doses or longer intervals between doses because they can't eliminate drugs as efficiently .
Pregnancy or nursing: Many drugs aren't safe for pregnant or nursing cats. Always tell your vet if your cat might be pregnant .
Other medications: Drug interactions can occur. Always tell your vet about everything your cat is taking, including supplements and flea preventatives .
Chronic conditions: Cats with conditions like hyperthyroidism or diabetes may need adjusted doses .
How to Use an Online Cat Drug Dose Calculator
Using one of these tools is straightforward, but accuracy matters:
Step 1: Weigh your cat accurately. The best way is to weigh yourself holding the cat, then weigh yourself alone and subtract. Digital scales are most accurate. Guessing leads to dosing errors .
Step 2: Enter your cat's weight in kilograms or pounds. Most calculators accept both, but kilograms are preferred for medical calculations.
Step 3: Select the medication from a list or enter the prescribed dose in mg/kg if you know it.
Step 4: Enter the medication concentration. For liquids, this is usually on the bottle (e.g., 50 mg/mL). For tablets, enter the tablet strength.
Step 5: Click calculate. The calculator shows the dose in mg, mL, or tablet fraction.
Step 6: Review the step-by-step explanation to ensure you understand how the number was derived.
Step 7: Double-check your inputs. A misplaced decimal can lead to a tenfold error.
Common Questions About Cat Dosing
Q: Can I use the same calculator for dogs and cats?
A: No. Dog and cat calculators are different because safe doses differ between species. Always use a species-specific calculator .
Q: What if my cat spits out part of the dose?
A: Never re-dose immediately. Contact your vet for guidance. Guessing how much was swallowed is risky .
Q: How do I give liquid medication to a reluctant cat?
A: Wrap your cat in a towel (burrito style), gently insert the syringe in the side of the mouth behind the canine teeth, and slowly depress the plunger. Aim for the cheek pouch, not straight down the throat .
Q: What if I miss a dose?
A: Give it as soon as you remember, unless it's almost time for the next dose. Never double up. When in doubt, ask your vet .
Q: Are compounded medications dosed the same?
A: Compounded medications may have different concentrations. Always verify the new concentration and recalculate doses .
The Responsibility of Cat Ownership
Bringing a cat into your life means accepting responsibility for their health and wellbeing. Part of that responsibility is ensuring they get the right medications at the right doses. It's easy to feel overwhelmed—veterinary medicine is complicated, and cats are masters at hiding illness.
But you don't have to figure it out alone. Your veterinarian is your partner in your cat's health. A Cat Drug Dose Calculator is a tool to help you follow their instructions accurately, not to replace their expertise. Used correctly, it prevents errors, reduces stress, and helps your cat recover faster.
The next time your cat needs medication, take a deep breath. Weigh them carefully. Check the prescription twice. Use a calculator to verify the dose. And if anything seems off—if the number looks wrong, if the cat seems worse, if you're just not sure—pick up the phone. Your vet would rather answer a quick question than treat a medication error.
Because at the end of the day, it's not about the numbers. It's about the purring creature curled up on your lap, trusting you to keep them safe and healthy. Getting the dose right is one of the most important ways you honor that trust.