Small Box Method (Most Accurate for Regular Rhythm)
Large Box Method (Quick Method for Regular Rhythm)
6-Second Method (Best for Irregular Rhythm/Atrial Fibrillation)
Count the number of 1mm squares between two consecutive R waves.
Count the number of 5mm squares between two consecutive R waves.
Count the number of peaks (R waves) in a 30-large-box span.
Estimated Heart Rate:
0 BPM
function toggleInputs() {
var method = document.getElementById('calcMethod').value;
document.getElementById('smallBoxInput').style.display = (method === 'small') ? 'block' : 'none';
document.getElementById('largeBoxInput').style.display = (method === 'large') ? 'block' : 'none';
document.getElementById('sixSecInput').style.display = (method === 'sixsec') ? 'block' : 'none';
document.getElementById('ecgResultContainer').style.display = 'none';
}
function calculateHR() {
var method = document.getElementById('calcMethod').value;
var hr = 0;
if (method === 'small') {
var smallBoxes = parseFloat(document.getElementById('smallBoxes').value);
if (smallBoxes > 0) {
hr = 1500 / smallBoxes;
}
} else if (method === 'large') {
var largeBoxes = parseFloat(document.getElementById('largeBoxes').value);
if (largeBoxes > 0) {
hr = 300 / largeBoxes;
}
} else if (method === 'sixsec') {
var complexes = parseFloat(document.getElementById('qrsComplexes').value);
if (complexes > 0) {
hr = complexes * 10;
}
}
if (hr > 0) {
var resultDiv = document.getElementById('ecgResultContainer');
var hrOutput = document.getElementById('hrOutput');
var hrCategory = document.getElementById('hrCategory');
hr = Math.round(hr);
hrOutput.innerHTML = hr + " BPM";
resultDiv.style.display = 'block';
if (hr < 60) {
hrCategory.innerHTML = "Bradycardia ( 100) {
hrCategory.innerHTML = "Tachycardia (>100 BPM)";
hrCategory.style.color = "#c0392b";
} else {
hrCategory.innerHTML = "Normal Heart Rate (60-100 BPM)";
hrCategory.style.color = "#27ae60";
}
} else {
alert("Please enter a valid positive number.");
}
}
How to Calculate Heart Rate on a 12-Lead ECG
Calculating the heart rate from an electrocardiogram (ECG) is a fundamental skill in clinical medicine and cardiology. Standard ECG paper moves at a constant speed of 25 mm per second. This allows us to use the physical distance on the paper to determine the time between beats.
1. The Small Box Method (1500 Method)
This is the most accurate method for regular rhythms. Because there are 1,500 small boxes (1mm) in one minute of ECG paper, you divide 1500 by the number of small boxes between two R waves (the R-R interval).
Formula: 1500 / # of small boxes = Heart Rate
Example: If there are 20 small boxes between R waves, 1500 / 20 = 75 BPM.
2. The Large Box Method (300 Method)
This is a quicker version of the small box method, useful for rapid bedside assessment. There are 300 large boxes (5mm) in one minute of ECG paper.
Formula: 300 / # of large boxes = Heart Rate
Example: If there are 4 large boxes between R waves, 300 / 4 = 75 BPM.
3. The 6-Second Method
When the heart rhythm is irregular (such as in Atrial Fibrillation), the R-R interval varies. Using the box methods will give an incorrect reading. Instead, we look at a longer period of time.
Step 1: Identify a 6-second strip (this is usually 30 large boxes).
Step 2: Count the total number of QRS complexes (R-wave peaks) within that strip.
Step 3: Multiply that number by 10 to get the beats per minute.