Drug Calculation Test Practice & Dosage Calculator
This resource is designed for nursing students and healthcare professionals to master medication dosage calculations. Use our calculators to verify your math and review the practice test questions below.
1. Basic Dosage (Desired/Have)
2. IV Flow Rate (mL/hr)
3. IV Drip Rate (gtt/min)
Drug Calculation Test Questions and Answers
Prepare for your pharmacology exams with these common drug calculation scenarios. Understanding the formulas is key to patient safety.
Question 1: The physician orders 0.5 g of Cephalexin. The pharmacy provides 250 mg capsules. How many capsules should be administered?
Question 2: Infuse 1 liter of Normal Saline over 12 hours. What is the flow rate in mL/hr?
Show Answer
Answer: 83.3 mL/hr. (1000 mL / 12 hr = 83.33).
Question 3: A patient is prescribed 15 mg/kg of a medication. The patient weighs 70 kg. What is the total dose?
Show Answer
Answer: 1,050 mg. (15 mg x 70 kg = 1050 mg).
Question 4: You need to administer 500 mL of D5W over 4 hours with a drop factor of 20 gtt/mL. What is the drip rate in gtt/min?
Show Answer
Answer: 42 gtt/min. (500 mL x 20 / 240 minutes = 41.66).
How to Solve Drug Calculation Questions
Drug calculations in nursing exams usually fall into three main categories: tablet/liquid dosages, IV flow rates, and drip rates. Mastering these formulas is essential for passing the NCLEX and ensuring medication accuracy.
The Basic Formula (The "Universal Formula")
For most oral medications or injections, use this formula:
(Desired / Have) × Quantity = X
Desired: The dose the doctor ordered.
Have: The dosage strength available on the label.
Quantity: The form the drug comes in (1 tablet, 5 mL, etc.).
IV Flow Rates and Drip Rates
When calculating IV fluids, you must distinguish between flow rate (mL per hour) and drip rate (drops per minute).
Flow Rate (mL/hr): Total Volume (mL) ÷ Total Time (hr)
Drip Rate (gtt/min): [Total Volume (mL) × Drop Factor (gtt/mL)] ÷ Total Time (min)
Common Conversions to Remember
Accuracy starts with unit conversion. Memorize these standard equivalents:
1 gram (g) = 1,000 milligrams (mg)
1 milligram (mg) = 1,000 micrograms (mcg)
1 kilogram (kg) = 2.2 pounds (lb)
1 teaspoon (tsp) = 5 milliliters (mL)
1 tablespoon (tbsp) = 15 milliliters (mL)
1 ounce (oz) = 30 milliliters (mL)
function calculateDosage() {
var desired = parseFloat(document.getElementById('desiredDose').value);
var hand = parseFloat(document.getElementById('doseOnHand').value);
var vehicle = parseFloat(document.getElementById('vehicle').value);
var resultDiv = document.getElementById('dosageResult');
if (isNaN(desired) || isNaN(hand) || isNaN(vehicle) || hand === 0) {
resultDiv.style.display = 'block';
resultDiv.innerHTML = 'Please enter valid numbers. Dose on hand cannot be zero.';
resultDiv.style.color = '#c0392b';
return;
}
var amount = (desired / hand) * vehicle;
resultDiv.style.display = 'block';
resultDiv.style.color = '#2c3e50';
resultDiv.innerHTML = 'Amount to Administer: ' + amount.toFixed(2) + ' (units/mL/tabs)';
}
function calculateIVRate() {
var volume = parseFloat(document.getElementById('ivVolume').value);
var hours = parseFloat(document.getElementById('ivHours').value);
var resultDiv = document.getElementById('flowResult');
if (isNaN(volume) || isNaN(hours) || hours === 0) {
resultDiv.style.display = 'block';
resultDiv.innerHTML = 'Please enter valid volume and hours.';
resultDiv.style.color = '#c0392b';
return;
}
var rate = volume / hours;
resultDiv.style.display = 'block';
resultDiv.style.color = '#2c3e50';
resultDiv.innerHTML = 'Flow Rate: ' + rate.toFixed(1) + ' mL/hr';
}
function calculateDripRate() {
var volume = parseFloat(document.getElementById('dripVolume').value);
var factor = parseFloat(document.getElementById('dripFactor').value);
var minutes = parseFloat(document.getElementById('dripMinutes').value);
var resultDiv = document.getElementById('dripResult');
if (isNaN(volume) || isNaN(factor) || isNaN(minutes) || minutes === 0) {
resultDiv.style.display = 'block';
resultDiv.innerHTML = 'Please enter valid inputs.';
resultDiv.style.color = '#c0392b';
return;
}
var dripRate = (volume * factor) / minutes;
resultDiv.style.display = 'block';
resultDiv.style.color = '#2c3e50';
resultDiv.innerHTML = 'Drip Rate: ' + Math.round(dripRate) + ' gtt/min';
}
function toggleAnswer(id) {
var element = document.getElementById(id);
if (element.style.display === 'block') {
element.style.display = 'none';
} else {
element.style.display = 'block';
}
}