Enter 0 or leave blank if not applicable (e.g., for tablets/capsules)
Understanding Dosage Calculations
Accurate dosage calculation is a critical skill for healthcare professionals, ensuring patient safety and therapeutic effectiveness. This tool helps practice common scenarios encountered in medication administration.
The Core Formula
The fundamental principle behind most dosage calculations can be simplified into a variation of the following formula, often remembered by the mnemonic "Have, Want, Have Over Seen":
(Ordered Dose / Amount on Hand) * Quantity on Hand = Dosage to Administer
Let's break down the inputs for this calculator:
Ordered Dose: The total amount of medication the physician has prescribed for the patient. (e.g., 250 mg)
Ordered Dose Unit: The unit of measurement for the ordered dose. Consistency is key! (e.g., mg)
Form Available: The physical form of the medication you have on hand. (e.g., tablet, capsule, vial)
Amount Available: The quantity of the active ingredient present in the form available. (e.g., 500 mg is available per tablet, or 500 mg is present in 1 mL of solution)
Amount Available Unit: The unit of measurement for the amount available. This MUST be the same unit as the Ordered Dose for simple calculations. (e.g., mg)
Vehicle: This is relevant for liquid medications or when reconstitution is required. It represents the volume (usually in mL) in which the 'Amount Available' is contained or dissolved. If you have tablets or capsules, this field is not needed (enter 0 or leave blank). (e.g., If you have 500mg/5mL concentration, the vehicle is 5 mL).
How the Calculator Works
This calculator adapts the core formula based on the type of medication and whether a vehicle is involved:
For Solids (Tablets/Capsules): The calculator determines the number of tablets or capsules to administer.
Number of Tablets/Capsules = (Ordered Dose / Amount Available)
For Liquids (or Reconstituted Medications): The calculator determines the volume (in mL) to draw up and administer.
Volume to Administer (mL) = (Ordered Dose / Amount Available) * Vehicle
The calculator ensures the units for 'Ordered Dose' and 'Amount Available' are the same for accurate ratio calculation. If they differ (e.g., ordered in grams, available in milligrams), you would typically convert first before using the tool, or ensure the input fields accurately reflect the relationship.
Common Scenarios & Use Cases
Oral Medications: Calculating the number of tablets or capsules based on prescribed mg and available strengths.
Intravenous (IV) Fluids: Calculating infusion rates or total volume based on prescribed dosage and available concentration.
Injectable Medications: Determining the correct volume to draw from a vial based on ordered units/mg and vial concentration (mg/mL).
Pediatric Dosing: Adjusting adult dosages or calculating doses based on weight (though weight-based calculations often require additional inputs not included in this basic tool).
Important Considerations
Unit Conversion: Always be mindful of units (mg, g, mcg, mL, L, units, mEq). If your ordered dose unit and available amount unit don't match, you must perform conversions before using this calculator or ensure your inputs reflect the conversion (e.g., if ordered 1g and available 500mg/tablet, input '1000' for ordered dose and '500' for amount available if units are both 'mg').
Safety First: This tool is for practice and educational purposes. Always double-check your calculations, verify against drug references, and follow institutional protocols. Never rely solely on a calculator for critical patient care decisions.
function calculateDosage() {
var orderedDose = parseFloat(document.getElementById("orderedDose").value);
var orderedDoseUnit = document.getElementById("orderedDoseUnit").value.trim();
var formAvailable = document.getElementById("formAvailable").value.trim().toLowerCase();
var amountAvailable = parseFloat(document.getElementById("amountAvailable").value);
var amountAvailableUnit = document.getElementById("amountAvailableUnit").value.trim().toLowerCase();
var vehicle = parseFloat(document.getElementById("vehicle").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// — Input Validation —
if (isNaN(orderedDose) || isNaN(amountAvailable) || orderedDose <= 0 || amountAvailable 0) {
// Calculation for liquid forms
if (isNaN(vehicle) || vehicle <= 0) {
resultDiv.innerHTML = "Error: Vehicle (mL) is required for liquid dosage calculations.";
return;
}
calculatedDosage = (orderedDose / amountAvailable) * vehicle;
unit = " mL";
if (isNaN(calculatedDosage)) {
resultDiv.innerHTML = "Error: Could not calculate dosage for liquid form.";
return;
}
} else {
resultDiv.innerHTML = "Error: Unable to determine calculation type based on 'Form Available'. Please specify tablet, capsule, mL, or solution.";
return;
}
// — Display Result —
// Round to a reasonable number of decimal places, typically 1 or 2 for mL, whole numbers for tablets
var displayDosage;
if (unit.includes("mL")) {
displayDosage = calculatedDosage.toFixed(1); // 1 decimal place for mL
} else {
displayDosage = calculatedDosage.toFixed(0); // Whole number for tablets/capsules
}
resultDiv.innerHTML = "Administer: " + displayDosage + unit + "";
}