Educational reference only. This tool performs the standard unit conversion from a weight-based dose to a pump rate — it does not verify that the dose itself is appropriate, and it is not a drug order. Confirm the correct dose range for the drug and patient, double-check the drug concentration on the label, and verify the calculated rate against your practice protocol or a second source before administering. CRI orders must reflect the individual patient and the attending veterinarian’s judgment.
Enter a weight, dose, and drug concentration above to calculate the infusion rate in ml/hr.
How This Calculator Works
A constant rate infusion (CRI) delivers a drug continuously at a dose scaled to body weight. To set a pump you must convert that dose into a volume rate — millilitres per hour — using the concentration of the drug in the line. The tool supports the two units CRIs are most commonly written in:
- mcg/kg/min — ml/hr = (dose × weightkg × 60) ÷ (concentrationmg/ml × 1000). The ×60 converts per-minute to per-hour; the ÷1000 converts micrograms to milligrams (1 mg = 1000 mcg) so units match the concentration.
- mg/kg/hr — ml/hr = (dose × weightkg) ÷ concentrationmg/ml. No time or unit conversion is needed because the dose is already per hour and in milligrams.
Enter the concentration of the fluid the pump actually delivers (the final in-bag concentration if you diluted the drug), and the calculator shows the worked substitution plus the total drug delivered per hour as a cross-check.
Worked Examples
A 20 kg patient, dosed at 10 mcg/kg/min, drug concentration 4 mg/ml:
(10 × 20 × 60) ÷ (4 × 1000) = 12000 ÷ 4000 = 3 ml/hr
A 10 kg patient, dosed at 2 mg/kg/hr, drug concentration 20 mg/ml:
(2 × 10) ÷ 20 = 20 ÷ 20 = 1 ml/hr
Frequently Asked Questions
What is the formula to convert a CRI dose into ml/hr?
For a mcg/kg/min dose: ml/hr = (dose × weight in kg × 60) ÷ (concentration in mg/ml × 1000). The ×60 converts per-minute to per-hour and the ÷1000 converts mcg to mg to match the concentration. For a mg/kg/hr dose it is simpler: ml/hr = (dose × weight in kg) ÷ concentration in mg/ml.
Why does the mcg/kg/min formula divide by 1000?
Because the dose is in micrograms but drug concentration is in milligrams per ml, and 1 mg = 1000 mcg. Dividing by 1000 converts the micrograms of drug into milligrams so the units cancel correctly and the result comes out in ml/hr.
Can I use this for both microgram and milligram dosing?
Yes. Pick the unit that matches how the drug is dosed — mcg/kg/min for potent agents dosed by the minute (many analgesic and vasoactive infusions) or mg/kg/hr for drugs dosed by the hour. The calculator applies the matching conversion and shows the full substitution so you can verify it.
What concentration should I enter?
Enter the concentration of the fluid the pump is actually delivering, in mg/ml. If you dilute a drug into a bag, that is the final in-bag concentration (total mg added ÷ total bag volume in ml), not the concentration of the original vial. Always double-check the label and your dilution math.
Does this calculator check that my dose is safe?
No. It only converts a dose you supply into a pump rate — it does not know the safe dose range for any drug or patient. Confirm the dose against a current formulary, verify the result against your practice protocol or a second source, and apply clinical judgment before administering.
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