Drug Dose Calculation Formula

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Drug Dosage Calculation Calculator

Accurate D/H × Q Formula for Clinical Practice

The amount of medication ordered by the physician (mg, mcg, g).
The dosage strength available on the label.
The quantity the dose is contained in (mL, tablets, caps).
Amount to Administer:

Understanding the Drug Dosage Formula

Dosage calculation is a critical skill for nursing and medical professionals. The most common method used is the D/H × Q formula, which ensures that the correct volume or quantity of medication is delivered based on the stock available.

The Formula Defined:

(Desired Dose / Stock Strength) × Stock Volume = Amount to Administer

  • D (Desired Dose): The amount of medication prescribed by the healthcare provider.
  • H (Have/Stock Strength): The dosage of the medication that is currently available or in stock.
  • Q (Quantity/Volume): The form in which the stock dose comes (e.g., one tablet, 5 mL of liquid).

Example Calculation

Suppose a physician orders 150 mg of a medication. On hand, you have a vial labeled 75 mg / 2 mL.

  1. Desired (D): 150 mg
  2. Have (H): 75 mg
  3. Quantity (Q): 2 mL
  4. Calculation: (150 / 75) × 2 = 4 mL

The nurse should administer 4 mL of the medication.

Safety Tips for Dosage Calculations

  • Unit Consistency: Always ensure the Desired Dose and Stock Strength are in the same units (e.g., both in mg, not one in g and one in mg). If they differ, convert them before using the formula.
  • Double Check: Always perform a manual check or have a colleague verify high-risk medications.
  • Zeros: Never use a trailing zero (e.g., write 5 mg, not 5.0 mg) and always use a leading zero (e.g., write 0.5 mg, not .5 mg) to prevent dosing errors.
function calculateDrugDose() { var desired = parseFloat(document.getElementById("desiredDose").value); var stock = parseFloat(document.getElementById("stockStrength").value); var volume = parseFloat(document.getElementById("stockVolume").value); var resultDiv = document.getElementById("dosageResult"); var output = document.getElementById("doseOutput"); var explanation = document.getElementById("formulaExplanation"); if (isNaN(desired) || isNaN(stock) || isNaN(volume) || stock <= 0 || volume <= 0) { alert("Please enter valid positive numbers for all fields."); resultDiv.style.display = "none"; return; } var dosage = (desired / stock) * volume; // Format the number: round to 2 decimal places if necessary var formattedDosage = Math.round(dosage * 100) / 100; resultDiv.style.display = "block"; output.innerText = formattedDosage + " (Quantity/Volume)"; explanation.innerText = "Calculation: (" + desired + " / " + stock + ") × " + volume + " = " + formattedDosage; }

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