Use these nursing scenarios to sanity-check the formula, then load the same values back into the calculator with one click.
Antibiotic
A provider orders 500 mg of amoxicillin suspension. The bottle label reads 250 mg per 5 mL.
This is the most common oral-suspension pattern used for pediatric antibiotics.
Microgram Order
The order is written in micrograms, but the stock label is in milligrams, so the units must be aligned first.
Converting mg and mcg before dividing prevents a 1000-fold medication error.
Household Teaching
A discharge instruction needs a household-measure equivalent after you confirm the clinical volume in milliliters.
Household equivalents are helpful for teaching, but the charted and dispensed dose should still be measured accurately in mL.
The standard nursing formula for calculating the volume of a liquid medication to administer orally. D is the desired dose, H is the available (have) dose, and Q is the volume containing H.
X (volume) = (D / H) × Q
Enter the desired dose ordered by the prescriber, the available dose on the medication label, and the volume that contains the available dose. The calculator divides D by H, multiplies by Q, and returns the volume to administer in your chosen output unit (mL, L, tsp, or tbsp).
A provider orders 500 mg of amoxicillin suspension. The pharmacy supplies a bottle labeled 250 mg per 5 mL. How many mL should the nurse administer?
Always use a calibrated oral syringe or medicine cup — household spoons are not precise enough for medication dosing.
P.O. (Latin: per os) means by mouth. This calculator covers oral liquid medications including solutions, syrups, and suspensions. The D and H values must be in the same mass unit before division. This calculator auto-converts between mg, g, and mcg.
Use the formula X = (D / H) × Q. Divide the desired dose by the available dose, then multiply by the quantity (volume). For example, if the order is 500 mg and the bottle reads 250 mg/5 mL, you get (500/250) × 5 = 10 mL.
Both use the same D/H × Q formula. For tablets, Q is the number of tablets per dose unit (usually 1) and the answer is in tablets. For liquids, Q is a volume (e.g., 5 mL) and the answer is in milliliters, teaspoons, or tablespoons.
Yes — use the Result Unit dropdown to display the answer in teaspoons (tsp) or tablespoons (tbsp). One teaspoon is approximately 5 mL. For clinical accuracy, always use a calibrated measuring device rather than household spoons.
Liquid medication calculations use the same nursing formula as tablets: X = (D / H) × Q. The difference is that Q is a liquid volume such as 5 mL, and the answer is a volume to measure and administer.
Chart and verify medication doses in milliliters whenever possible. Household units like teaspoons can be useful for patient teaching, but milliliters are safer and more precise for preparation, administration, and documentation.
Liquid calculations deserve extra attention when the order and stock strength use different units, when the final volume is very small, when the patient is pediatric, or when the medication has a narrow therapeutic range. Those are all situations where a simple conversion mistake can become clinically significant.
Reference:
Institute for Safe Medication Practices. Oral liquid medications: dosage devices and metric measurement guidance. ISMP Medication Safety Alerts and consumer-safety recommendations. https://www.ismp.org/