Veterinary Dose Calculator
How to useFill in the fields to see a result.
You do not medicate a whole house before assessing it. FAHS is the flock assessment that comes before this calculation and measures what it did: the template used, and the scores before and after.
Start a flock assessmentHow each calculation is made
The arithmetic behind every calculator, a worked example, and the one mistake each is most often used to make.
How do you calculate a drug dose from an animal's weight?
Multiply the animal's weight by the dose prescribed per kilogram to get the total amount of drug, then divide by the product's concentration to get the volume to draw. A weight in pounds is converted to kilograms first, by multiplying by 0.453592. A concentration given as a percentage is read as w/v, so 1% is 10 mg/ml. Where the dose and the concentration use the same arbitrary unit, the units cancel and no conversion to milligrams is needed at all.
Formula
total drug = weight (kg) × dose per kg volume (ml) = total drug ÷ concentration (mg/ml)
Worked example
A 10 kg dog at 5 mg/kg of a product containing 2 mg/ml needs 10 × 5 = 50 mg, and 50 ÷ 2 = 25.00 ml. That volume is far above any single-site limit, so it would have to be split across sites or the numbers rechecked.
What goes wrong
Per-injection-site limits are much lower than most people expect and vary by species and route: about 1 ml intramuscularly in a cat, 3 ml per site in a dog, 10 ml per site in cattle. Subcutaneous limits are far higher than intramuscular ones. At the other end, a volume below 0.1 ml should not be drawn directly — a 21G or 23G needle hub holds about 0.05 ml of dead space on its own.
Sources: Diehl KH et al., J Appl Toxicol 2001;21(1):15–23; IQ 3Rs Leadership Group, Recommended Dose Volumes for Common Laboratory Animals, 2016; Beef Quality Assurance National Manual; WHO Technical Report Series No. 970 (2012) Annex 5; Cambruzzi & Macfarlane, Vet Anaesth Analg 2021;48(4):532–536.
How much medication goes into a flock's drinking water?
Multiply the number of animals by their average weight to get live weight, multiply that by the dose per kilogram to get the total active ingredient, then divide by the product's strength to get how much product to weigh out. A powder's strength is a percentage: 97% means 970 mg of active per gram. If the dose is given as a concentration in the water rather than per kilogram of animal, it is multiplied by the volume of water being medicated instead. With a proportioner pump, the stock tank must hold the day's water multiplied by the pump ratio, so it runs out exactly when the water does.
Formula
live weight (kg) = head count × average weight total active (mg) = live weight × dose (mg/kg) powder (g) = total active ÷ (percent × 10) stock tank (L) = daily water × pump ratio
Worked example
12,000 birds averaging 0.5 kg is 6,000 kg of live weight. At 20 mg/kg that is 120,000 mg of active, which a 97% powder supplies in 123.7 g. With a metered 1,080 L of water a day and a 1% pump, the stock tank holds 10.8 L.
What goes wrong
This calculator will not estimate the flock's water for you, and that is deliberate. No breeder guide or extension service publishes intake as a share of body weight — the "18% of body weight" figure in circulation is a misreading of a lifetime water-to-feed figure — intake falls as a share of weight with age, and the two published temperature coefficients differ by a factor of two. Install a meter. Separately, a powder's maximum solubility is a property of the specific product, printed on its label, and ranges from 1 to 6 g/L across five authorised amoxicillin powders alone.
Sources: Aviagen Brief, Water Utilization in Broilers, Jan 2025; Ritz & Fairchild, UGA Extension B1301, rev. 2015; Williams, Tabler & Watkins, J Appl Poult Res 2013;22(4):934–941; Tabler, Wells & Zhai, Mississippi State Extension P2742, 2021; EMA CVMP EMEA/CVMP/540/03 Rev.1.
How much premix goes into a batch of medicated feed?
Multiply the batch size in tonnes by the target grams of active per tonne, then divide by the premix's strength in grams of active per kilogram. One part per million in feed is one milligram per kilogram, which is one gram per tonne — a unit identity, not a conversion. The calculator also returns the inclusion rate, the fraction of the batch the premix represents, because that number decides whether the premix can be mixed in directly at all.
Formula
premix (kg) = feed (t) × dose (g/t) ÷ premix strength (g/kg) inclusion rate (%) = premix ÷ feed × 100
Worked example
A 2 tonne batch at 400 g of active per tonne needs 800 g of active. A premix at 194 g/kg supplies that in 4.12 kg — an inclusion rate of 0.21%, low enough that it must be pre-blended into a carrier batch first.
What goes wrong
A few kilograms of premix tipped into a multi-tonne mixer does not distribute. Animals at one end of that distribution get nothing and at the other end get a lethal dose. Blend it into a small carrier batch of the same feed first, then add that to the mixer. Note also that "ton" here is the metric tonne: a US short ton is 907 kg, which makes 1 g per short ton equal 1.10 ppm, not 1.00.
Sources: Regulation (EU) 2019/4 Art. 6; Regulation (EC) 183/2005 Annex II; 21 CFR Parts 225 and 226; Dunmire, Stark & Paulk, KSU Quality Feed Manufacturing Guide, 2021, after Herrman & Behnke MF-1172 (1994); GMP+ TS1.11 (2022).
How do you work out a bath treatment for a pond or tank?
Work out the water volume first, then the product. A rectangular pond is length times width times average depth; a circular tank is pi times the radius squared, times depth. A cubic metre of fresh water is 1,000 litres. One part per million is one milligram per litre, so the pure active needed in grams is the volume in litres times the target concentration, divided by a thousand. If the product is not pure, divide again by its percentage.
Formula
volume (m³) = length × width × AVERAGE depth litres = volume × 1000 pure active (g) = litres × mg/L ÷ 1000 product (g) = pure active ÷ (percent ÷ 100)
Worked example
A pond 40 m by 20 m with an average depth of 0.3 m holds 240 m³, or 240,000 litres. At a target of 2.5 mg/L that needs 600 g of pure product.
What goes wrong
Depth means the average across the whole pond, taken from soundings on a grid, not the reading at the deepest point. A sloping floor measured at the drain can double the computed volume, and the dose follows it — and the failure is asymmetric: too little is merely ineffective, too much kills the crop. This calculator also refuses outright to dose a raceway or any flow-through system, because there the product is metered in at the inflow against flow rate, and a static volume is simply the wrong calculation.
Sources: Masser & Jensen, SRAC Publication 103 and 410, Southern Regional Aquaculture Center; Burtle & Shelton, UGA Extension B866, rev. 2017; Bowker & Trushenski (eds.), Guide to Using Drugs, Biologics, and Other Chemicals in Aquaculture, American Fisheries Society, rev. 2019.
How much drug goes into an IV bag for a constant rate infusion?
Work out how fast the fluid runs, then how long the bag lasts at that rate, then how much drug is needed to cover exactly that long. Putting in enough for the lifetime of the bag is what keeps the delivered concentration constant. A dose in micrograms per kilogram per minute is multiplied by weight, by sixty, and by the hours the bag lasts, then divided by a thousand to reach milligrams; dividing by the stock concentration gives the volume to add.
Formula
rate (ml/h) = maintenance (ml/kg/h) × weight (kg) bag hours = bag volume ÷ rate drug (mg) = dose (mcg/kg/min) × weight × 60 × hours ÷ 1000 volume to add (ml) = drug ÷ stock (mg/ml)
Worked example
A 20 kg dog at 2 ml/kg/h runs at 40 ml/h, so a 500 ml bag lasts 12.5 hours. Delivering 2 mcg/kg/min for that long takes 30 mg of drug, which is 0.300 ml of a 100 mg/ml stock.
What goes wrong
Withdraw a volume of fluid equal to the drug before adding it, every time — adding without withdrawing changes the volume the pump is metering against. There is no threshold at which this starts to matter; the widely repeated ten percent rule is an institution-local convention that different hospitals apply in opposite directions. And a manufacturer's bag is overfilled by three to thirty-six percent of its printed volume, so the drug's concentration inside a sealed bag cannot be calculated at all — only the total dose it contains. An exact concentration needs an empty container.
Sources: Cohen MR & Smetzer JL, Hosp Pharm 2014;49(3):221–226; ISMP Canada Safety Bulletin 13(7), 2013; Ko E et al., J Korean Med Sci 2022;37(49):e345; Lukasik V, Constant Rate Infusions in Small Animal Anesthesia, WSAVA Congress 2015.
What do you do when a dose is too small to draw into a syringe?
Dilute it to a volume you can actually measure. Divide the dose by the stock concentration to see how small the neat volume really is, then work out how many times it has to be diluted to reach a volume you can draw. Rather than chasing that tiny neat volume, draw a larger, measurable amount of stock and dilute it by the same factor: the concentration of the mixed solution falls in proportion, and the dose you finally draw carries exactly the milligrams prescribed.
Formula
neat volume (ml) = dose (mg) ÷ stock (mg/ml) dilution factor = target volume ÷ neat volume mixed volume = stock drawn × dilution factor diluent = mixed volume − stock drawn
Worked example
A 0.2 mg dose of a 50 mg/ml product is 0.004 ml of neat drug — unmeasurable. To inject 0.5 ml instead, that is a 125-fold dilution: draw 0.1 ml of stock into a sterile vial, add 12.4 ml of diluent, mix, and draw 0.5 ml. The mixed solution is 0.4 mg/ml, so 0.5 ml carries the 0.2 mg prescribed.
What goes wrong
Mix in a vial and draw from the mixed solution. Never layer drug and diluent inside one syringe: the dead space in a standard needle hub is around 0.05 ml, which at these doses can exceed the entire prescription. A syringe also measures reliably only down to roughly a fifth of its labelled capacity — 0.2 ml in a 1 ml syringe, 0.06 ml in a 0.3 ml insulin syringe.
Sources: Jordan MA et al., Hosp Pharm 2021;56(3):165–171; Cambruzzi & Macfarlane, Vet Anaesth Analg 2021;48(4):532–536; Malerba E et al., J Vet Intern Med 2021;35(3):1255–1264; WHO Technical Report Series No. 970 (2012) Annex 5.
Important notes
This calculator converts and divides. It holds no dosage database and no species safety limits. Always consult the attending veterinarian and check the product leaflet before administering any dose.