Accurate medication dosage is crucial for patient safety and treatment effectiveness. This calculator assists in determining the appropriate amount of medication to administer based on patient weight, the prescribed dosage per unit of weight, and the concentration of the medication available.
How it Works:
Patient Weight: Enter the patient's weight in kilograms (kg) or pounds (lb). The calculator will automatically convert pounds to kilograms if necessary (1 lb = 0.453592 kg) for consistent calculations.
Medication Dosage (per weight): This is the prescribed dose of the medication per unit of body weight. Common units include milligrams per kilogram (mg/kg), micrograms per kilogram (mcg/kg), or international units per kilogram (units/kg). For example, a doctor might prescribe 5 mg/kg of a certain antibiotic.
Medication Concentration: This specifies how the medication is supplied. It's vital for determining the volume or number of units to administer. Examples include "250 mg per 5 mL" (for liquid suspensions), "500 mg per tablet" (for oral medications), or "10,000 units per mL" or "50,000 units per vial" (for injectable medications).
The Calculation:
The primary calculation for the total medication amount is:
Total Medication Amount = Patient Weight (in kg) × Medication Dosage (per kg)
For example, if a patient weighs 70 kg and the prescribed dose is 5 mg/kg:
Total Medication Amount = 70 kg × 5 mg/kg = 350 mg
This calculated 350 mg is the target dose. The next step, which this calculator provides, is to determine the practical volume or number of units to administer based on the medication's concentration.
Determining Volume/Units to Administer:
Once the Total Medication Amount is calculated, you use the concentration to find the volume (e.g., mL) or number of units to give. The formula is:
Volume/Units to Administer = Total Medication Amount / Concentration Value
Example Scenarios:
Scenario 1: Liquid Medication
Patient Weight: 70 kg
Dosage: 5 mg/kg
Concentration: 250 mg per 5 mL
Calculated Total Medication Amount: 70 kg * 5 mg/kg = 350 mg
Volume to Administer: 350 mg / (250 mg / 5 mL) = 350 mg * (5 mL / 250 mg) = 7 mL
Scenario 2: Injectable Medication (Vial)
Patient Weight: 15 kg
Dosage: 100,000 units/kg
Concentration: 50,000 units per mL
Calculated Total Medication Amount: 15 kg * 100,000 units/kg = 1,500,000 units
Volume to Administer: 1,500,000 units / (50,000 units/mL) = 30 mL
Scenario 3: Pediatric Dose (Weight-Based)
Patient Weight: 25 lb
Dosage: 10 mcg/kg
Concentration: 50 mcg per mL
Convert weight: 25 lb * 0.453592 kg/lb ≈ 11.34 kg
Calculated Total Medication Amount: 11.34 kg * 10 mcg/kg ≈ 113.4 mcg
Volume to Administer: 113.4 mcg / (50 mcg/mL) ≈ 2.27 mL
Important Considerations:
Always double-check your calculations.
Ensure the medication concentration is correctly identified.
Verify the units (mg, mcg, mL, units, etc.) are consistent.
Consult with a healthcare professional or pharmacist if you have any doubts. This calculator is a tool and should not replace professional medical advice.
Some medications require specific calculations based on age, body surface area (BSA), or other factors. This calculator is primarily for weight-based dosing.
function calculateDosage() {
var weightInput = document.getElementById("patientWeight");
var weightUnitSelect = document.getElementById("weightUnit");
var dosagePerWeightInput = document.getElementById("medicationDosagePerWeight");
var dosageUnitSelect = document.getElementById("dosageUnit");
var formulationInput = document.getElementById("medicationFormulation");
var calculatedDosageDiv = document.getElementById("calculatedDosage");
var dosageUnitsResultDiv = document.getElementById("dosageUnitsResult");
// Clear previous results
calculatedDosageDiv.textContent = "–";
dosageUnitsResultDiv.textContent = "–";
// Get input values
var patientWeight = parseFloat(weightInput.value);
var weightUnit = weightUnitSelect.value;
var medicationDosagePerWeight = parseFloat(dosagePerWeightInput.value);
var dosageUnit = dosageUnitSelect.value; // e.g., "mg/kg"
var formulationText = formulationInput.value.trim();
// — Input Validation —
if (isNaN(patientWeight) || patientWeight <= 0) {
alert("Please enter a valid patient weight.");
return;
}
if (isNaN(medicationDosagePerWeight) || medicationDosagePerWeight { value: 250, unit: "mg", volume: 1, volumeUnit: "mL" } ) —
var concentration = { value: NaN, unit: "", volume: NaN, volumeUnit: "" };
var formulationParts = formulationText.match(/(\d+(\.\d+)?)\s*(\w+)(?:\s*per\s*(\d+(\.\d+)?)\s*(\w+))?/);
if (!formulationParts) {
alert("Invalid medication concentration format. Please use formats like '250 mg/mL', '500 mg per tablet', or '50000 units/vial'.");
return;
}
concentration.value = parseFloat(formulationParts[1]);
concentration.unit = formulationParts[3].toLowerCase(); // Normalize to lowercase
if (formulationParts[5] && formulationParts[6]) { // If "per X Y" is present
concentration.volume = parseFloat(formulationParts[5]);
concentration.volumeUnit = formulationParts[6].toLowerCase();
} else { // Assume concentration is per 1 unit of volume if not specified
concentration.volume = 1;
// Try to infer a default volume unit if possible, otherwise leave it empty
if (formulationText.toLowerCase().includes('ml')) concentration.volumeUnit = 'ml';
else if (formulationText.toLowerCase().includes('l')) concentration.volumeUnit = 'l';
else if (formulationText.toLowerCase().includes('tablet')) concentration.volumeUnit = 'tablet';
else if (formulationText.toLowerCase().includes('capsule')) concentration.volumeUnit = 'capsule';
else if (formulationText.toLowerCase().includes('vial')) concentration.volumeUnit = 'vial';
// else keep empty if truly ambiguous
}
// — Validate Parsed Concentration —
if (isNaN(concentration.value) || concentration.value <= 0) {
alert("Invalid concentration value from the provided text.");
return;
}
if (concentration.unit !== primaryDosageUnit.toLowerCase()) {
alert("The concentration unit (" + concentration.unit + ") does not match the prescribed dosage unit (" + primaryDosageUnit + "). Please check your inputs.");
return;
}
if (isNaN(concentration.volume) || concentration.volume <= 0) {
alert("Invalid concentration volume from the provided text.");
return;
}
// — Calculate Final Volume/Units to Administer —
var amountToAdminister = totalMedicationAmount / concentration.value;
// Format the amount to administer appropriately
amountToAdminister = parseFloat(amountToAdminister.toFixed(2));
// — Display Results —
calculatedDosageDiv.textContent = amountToAdminister.toLocaleString(); // UsetoLocaleString for number formatting
// Construct the units string, e.g., "mL" or "tablets"
var unitsResult = "";
if (concentration.volumeUnit) {
// Handle plurals for units (simple case)
if (amountToAdminister === 1 && concentration.volumeUnit.endsWith('s')) {
unitsResult = concentration.volumeUnit.slice(0, -1); // Remove 's' if amount is 1
} else {
unitsResult = concentration.volumeUnit;
}
} else {
// Fallback if volume unit wasn't parsed or specified (e.g., for tablets)
// This might need more sophisticated logic based on common formulation types
if (formulationText.toLowerCase().includes('tablet')) unitsResult = "tablet(s)";
else if (formulationText.toLowerCase().includes('capsule')) unitsResult = "capsule(s)";
else if (formulationText.toLowerCase().includes('vial')) unitsResult = "vial(s)"; // less common to administer whole vials typically
else unitsResult = primaryDosageUnit; // fallback to the primary unit if unknown
}
// Adjust result if the concentration was specified per multiple units (e.g., 250mg per 5mL)
// The calculation above (amountToAdminister = totalMedicationAmount / concentration.value) gives the amount based on the concentration *value* unit.
// We need to scale it by the concentration *volume* unit.
var finalAmountToAdminister = amountToAdminister * (concentration.volume / 1); // Assuming concentration.volume is the number of volume units associated with concentration.value
calculatedDosageDiv.textContent = finalAmountToAdminister.toLocaleString(undefined, {
minimumFractionDigits: 2,
maximumFractionDigits: 2
});
// Re-evaluate unitsResult based on how the final amount is calculated
var finalUnitsString = "";
if (concentration.volumeUnit) {
// Handle potential pluralization better
if (Math.abs(finalAmountToAdminister – 1) < 0.01 && concentration.volumeUnit.endsWith('s')) {
finalUnitsString = concentration.volumeUnit.slice(0, -1); // Singular form
} else {
finalUnitsString = concentration.volumeUnit; // Plural or base form
}
} else {
// Fallback for units if volumeUnit wasn't parsed
if (formulationText.toLowerCase().includes('tablet')) finalUnitsString = "tablet(s)";
else if (formulationText.toLowerCase().includes('capsule')) finalUnitsString = "capsule(s)";
else if (formulationText.toLowerCase().includes('vial')) finalUnitsString = "vial(s)";
else finalUnitsString = primaryDosageUnit; // Use the primary unit if no volume unit is clear
}
dosageUnitsResultDiv.textContent = finalUnitsString;
}