Pet Medication Calculator: Calculate the Right Dosage for Your Pet

Your vet prescribed 5 mg/kg twice daily. Your dog weighs 18 pounds. Your medication is 250 mg tablets. How many tablets is that? Do you cut it? Is it 0.4 tablets or 0.8? This is the kind of math that matters and the kind you want to get right. The CalcHub Pet Medication Calculator does the conversion work for you — with the important caveat that you always verify with your veterinarian.

Always follow your veterinarian's specific dosing instructions. This calculator is a reference aid, not a substitute for professional veterinary advice.

How the Calculator Works

Enter:

• Pet's weight (lbs or kg)


• Prescribed dose (mg/kg or mg/lb)


• Medication concentration (mg per tablet, mg per mL for liquids)

The calculator returns: how many tablets, ml, or fraction of a tablet to administer per dose.

Common Dosing Examples

Tablet Dosing

A 35-lb dog prescribed amoxicillin at 10 mg/kg twice daily:

• 35 lbs ÷ 2.2 = 15.9 kg


• 15.9 kg × 10 mg/kg = 159 mg per dose


• Available in 250 mg tablets: 159/250 = 0.64 tablets ≈ round to nearest practical amount

Many vets prescribe in rounded weights precisely to avoid awkward fractions. When a dose works out to 0.64 tablets, your vet may have rounded the weight or dose intentionally.

Liquid Medication

A 7-lb cat prescribed metronidazole at 25 mg/kg daily:

• 7 lbs ÷ 2.2 = 3.18 kg


• 3.18 kg × 25 mg/kg = 79.5 mg per dose


• Available as 50 mg/mL suspension: 79.5 ÷ 50 = 1.59 mL

Common Weight-Based Dose Reference

Medication Type	Typical Dog Dose	Notes
Amoxicillin	10–20 mg/kg twice daily	Broad-spectrum antibiotic
Carprofen (pain/NSAID)	2.2 mg/kg twice daily	Never give ibuprofen to pets
Metronidazole	10–25 mg/kg twice daily	GI issues
Diphenhydramine (Benadryl)	1 mg/kg every 8 hrs	Antihistamine, vet approval first
Onsior	2 mg/kg once daily	Cat NSAID — DO NOT use dog NSAIDs in cats

Note: Cats have fundamentally different drug metabolism than dogs. Many medications safe for dogs are toxic to cats. Never administer dog medication to a cat without explicit vet guidance.

Fish Medication Dosing

Fish medications typically dose by tank volume, not fish weight. The calculator integrates with the aquarium volume calculator — enter your tank's water volume and the medication's dosing instructions (e.g., 1 teaspoon per 10 gallons) and it calculates the total amount needed.

When to Call the Vet Instead

The calculator is helpful for verifying your math, but always call your vet if:

• The calculated dose seems much higher or lower than expected


• Your pet's weight has changed significantly since the prescription was written


• You're considering giving a human medication to a pet (many are dangerous)


• Your pet shows adverse reactions to a medication

My tablet doesn't score easily into fractions. What should I do?

Use a pill cutter for halves and quarters. For smaller fractions, ask your vet if a different tablet strength, a liquid suspension, or a compounded medication is available.

Can I adjust my pet's dose at home if they seem to need more or less?

No. Dose adjustments require veterinary guidance. Under-dosing antibiotics contributes to resistance; overdosing analgesics and other medications can be harmful or fatal.

Related Calculators

• Pet Food Calculator — Some medications should be given with food
• Aquarium Volume Calculator — Accurate tank volume for fish medication dosing
• Pet Calorie Calculator — Nutrition supports recovery during medication courses