Estimate a starting dose, then confirm with your vet
Most medicines for dogs and cats are dosed by body weight, so a heavier animal needs proportionally more. This tool multiplies your pet’s weight by the published per-kilogram dose range for several commonly prescribed drugs and converts that to a liquid volume. It is a reference and sanity-check, not a prescription.
How it works
The calculation has two steps:
dose (mg) = weight (kg) × dose (mg per kg)
volume (mL) = dose (mg) ÷ concentration (mg per mL)Weight entered in pounds is first converted to kilograms by multiplying by 0.453592. The tool stores a low and a high milligrams-per-kilogram figure for each drug, so it reports a range rather than a single number, reflecting how vets titrate within a safe window. The volume assumes one common liquid or suspension concentration; if your product differs, recompute the volume from the milligram dose and your label’s strength.
Important safety notes
The list intentionally limits some drugs by species. Meloxicam and other NSAIDs appear for dogs only because repeated dosing in cats is dangerous. Doses shown are general references and do not account for the specific condition being treated, organ function, or drug interactions. Underdosing antibiotics breeds resistance and overdosing many drugs causes toxicity, so the exact regimen must come from your veterinarian.
Example
A 12 kg dog prescribed amoxicillin at 10 to 20 mg/kg needs 120 to 240 mg per dose every 12 hours. With a 50 mg/mL suspension that is 2.4 to 4.8 mL per dose.
About the drugs in this reference
Amoxicillin is a broad-spectrum penicillin antibiotic used for skin infections, urinary tract infections, and respiratory infections in both dogs and cats. The low end of the dose range (around 10 mg/kg) suits mild infections; the high end (20 mg/kg) is used for more resistant presentations. The full course — typically 7 to 14 days — must be completed even if the pet seems better, to avoid breeding resistant bacteria.
Metronidazole is an antiprotozoal and antibacterial drug used for gastrointestinal infections, giardia, and anaerobic bacterial infections. In dogs it is also sometimes used at low doses for inflammatory bowel disease as a secondary effect. Neurological side effects (wobbliness, head tilt, muscle tremors) can occur at higher doses, particularly in small breeds. If these appear, stop dosing and call your vet.
Meloxicam is a non-steroidal anti-inflammatory drug (NSAID) used for pain and inflammation in dogs — post-surgical pain, arthritis, musculoskeletal injury. It is restricted to dogs in this tool because oral meloxicam carries a black-box warning for cats in several jurisdictions: repeated oral dosing is associated with acute kidney injury and death in cats. A single one-time injection of meloxicam can be given to cats in a veterinary setting; repeated home dosing cannot.
Gabapentin is used in dogs and cats for neuropathic pain management, seizures, and as a sedation aid before stressful veterinary visits. Dosing for pain versus seizure control differs. Sedation doses for vet visits are often lower one-time amounts rather than ongoing therapeutic doses — confirm the intended use with your vet because the appropriate dose depends on the indication.
Famotidine is a stomach acid reducer (H2 antagonist) used to manage nausea, gastritis, and drug-induced stomach upset in dogs and cats. It is one of the most commonly used over-the-counter human medications given to pets, but the dose is weight-based rather than a fixed amount, so this tool helps avoid accidentally under- or over-dosing a small or large animal.
Reading a drug label — concentration and dose are different things
The most common source of dosing confusion is conflating the dose (mg/kg) with the concentration on the bottle (mg/mL). They are independent:
- The dose tells you how much drug per kilogram your pet needs.
- The concentration tells you how strong the liquid is.
A 50 mg/mL suspension and a 25 mg/mL suspension of the same drug require very different volumes to deliver the same milligram dose. Always check your label’s concentration before measuring, and use the milligram figure from this tool as the target — volume is just what you actually draw into the syringe or dropper to hit that target.