Best for regular rhythms. Count small boxes between two R waves.
Calculated Heart Rate0 BPM
function updateEcgLabels() {
var method = document.getElementById('calculationMethod').value;
var label = document.getElementById('inputLabel');
var hint = document.getElementById('methodDescription');
var input = document.getElementById('ecgInputValue');
// Reset input value when switching methods to avoid confusion
input.value = ";
document.getElementById('resultContainer').style.display = 'none';
if (method === '1500') {
label.innerText = 'Number of Small Squares between R-R';
hint.innerText = 'Precise method for regular rhythms. Count the tiny 1mm boxes.';
input.placeholder = 'e.g., 20';
} else if (method === '300') {
label.innerText = 'Number of Large Squares between R-R';
hint.innerText = 'Quick estimation for regular rhythms. Count the bold 5mm boxes.';
input.placeholder = 'e.g., 4';
} else if (method === '6sec') {
label.innerText = 'Number of QRS Complexes (R-Waves)';
hint.innerText = 'Standard method for irregular rhythms. Count R-waves in a 6-second strip.';
input.placeholder = 'e.g., 7';
}
}
function calculateHeartRate() {
var method = document.getElementById('calculationMethod').value;
var inputVal = parseFloat(document.getElementById('ecgInputValue').value);
var resultDisplay = document.getElementById('bpmResult');
var container = document.getElementById('resultContainer');
var interpretationDiv = document.getElementById('rhythmInterpretation');
var heartRate = 0;
// Validation
if (isNaN(inputVal) || inputVal <= 0) {
alert("Please enter a valid positive number.");
return;
}
// Calculation Logic
if (method === '1500') {
// Formula: 1500 divided by number of small squares
heartRate = 1500 / inputVal;
} else if (method === '300') {
// Formula: 300 divided by number of large squares
heartRate = 300 / inputVal;
} else if (method === '6sec') {
// Formula: Number of complexes multiplied by 10
heartRate = inputVal * 10;
}
// Round to nearest whole number
heartRate = Math.round(heartRate);
// Interpretation
var interpText = "";
var color = "#444";
if (heartRate < 60) {
interpText = "Bradycardia: Heart rate is slower than normal (= 60 && heartRate <= 100) {
interpText = "Normal Sinus Rhythm: Heart rate is within normal limits (60-100 BPM).";
color = "#2e7d32"; // Green
} else if (heartRate > 100) {
interpText = "Tachycardia: Heart rate is faster than normal (>100 BPM).";
color = "#d32f2f"; // Red
}
// Output
resultDisplay.innerText = heartRate + " BPM";
interpretationDiv.innerHTML = interpText;
interpretationDiv.style.color = color;
container.style.display = 'block';
}
Methods to Calculate Heart Rate on ECG
Interpreting an Electrocardiogram (ECG/EKG) is a fundamental skill in cardiology and emergency medicine. While modern machines provide automated analysis, manual verification is crucial for accuracy, especially when artifacts or arrhythmias are present. There are three primary methods used to calculate heart rate from an ECG strip, each suited for different clinical scenarios.
Note on Grid Sizing: Standard ECG paper moves at 25 mm/sec.
Small Square: 1mm x 1mm = 0.04 seconds.
Large Square: 5mm x 5mm = 0.20 seconds (contains 5 small squares).
1. The 1500 Method (The Small Square Method)
The 1500 method is the most precise technique for calculating heart rate, but it requires a regular rhythm. It relies on the specific measurement of time represented by the smallest grid boxes on the paper.
The Logic: Since the paper speed is 25mm/second, there are 1,500 small squares in one minute (25 mm/sec * 60 sec/min = 1500 mm/min).
Step 1: Identify two consecutive R-waves (the peak of the QRS complex).
Step 2: Count the number of small squares between them.
Step 3: Divide 1500 by this number.
Example: If there are 20 small squares between R-waves, the calculation is 1500 ÷ 20 = 75 BPM.
2. The 300 Method (The Large Square Method)
The 300 method is a quick estimation tool, ideal for rapid assessment in emergency situations. Like the 1500 method, it is only valid for regular rhythms.
The Logic: There are 300 large squares in one minute (since 1 large square = 0.20 seconds, and 60 ÷ 0.20 = 300).
Step 1: Locate an R-wave that falls on a heavy black line (start of a large square).
Step 2: Count the number of large squares until the next R-wave.
Step 3: Divide 300 by this number.
Sequence for Memorization: Many clinicians memorize the sequence for consecutive large lines: 300, 150, 100, 75, 60, 50. If the next R-wave lands on the 4th heavy line, the rate is 75 BPM.
3. The 6-Second Method
This is the only reliable method for calculating heart rate in irregular rhythms (such as Atrial Fibrillation). It provides a mean heart rate rather than a beat-to-beat calculation.
The Logic: A standard ECG strip usually contains markings indicating 3-second or 6-second intervals. By counting the beats in 6 seconds and multiplying by 10, you calculate the beats per 60 seconds (1 minute).
Step 1: Obtain a 6-second strip (usually indicated by 3 hash marks at the top of the paper, or 30 large squares).
Step 2: Count the number of complete QRS complexes (R-waves) within that 6-second period.
Step 3: Multiply that number by 10.
Example: If you count 8 QRS complexes in a 6-second strip, the heart rate is 8 x 10 = 80 BPM.
Clinical Ranges
Once you have calculated the heart rate, compare it to standard clinical ranges: