The 300 Method (Large Squares)
The 1500 Method (Small Squares)
The 6-Second Method (Irregular Rhythm)
Standard paper speed: 25 mm/sec
Calculated Heart Rate—
function updateInputLabel() {
var method = document.getElementById('calcMethod').value;
var label = document.getElementById('dynamicLabel');
var input = document.getElementById('ecgInput');
if (method === '300') {
label.innerText = "Number of Large Squares between R-waves";
input.placeholder = "e.g., 4";
} else if (method === '1500') {
label.innerText = "Number of Small Squares between R-waves";
input.placeholder = "e.g., 20";
} else if (method === '6sec') {
label.innerText = "Number of QRS Complexes in 6 Seconds (30 Large Squares)";
input.placeholder = "e.g., 7″;
}
// Clear result when method changes
document.getElementById('result-container').style.display = 'none';
input.value = ";
}
function calculateHeartRate() {
var method = document.getElementById('calcMethod').value;
var inputValue = parseFloat(document.getElementById('ecgInput').value);
var resultContainer = document.getElementById('result-container');
var bpmDisplay = document.getElementById('bpmResult');
var interpDisplay = document.getElementById('interpretation');
// Basic validation
if (isNaN(inputValue) || inputValue <= 0) {
alert("Please enter a valid positive number.");
return;
}
var heartRate = 0;
// Calculation Logic
if (method === '300') {
// HR = 300 / large squares
heartRate = 300 / inputValue;
} else if (method === '1500') {
// HR = 1500 / small squares
heartRate = 1500 / inputValue;
} else if (method === '6sec') {
// HR = count * 10
heartRate = inputValue * 10;
}
// Round to nearest whole number
heartRate = Math.round(heartRate);
// Display BPM
bpmDisplay.innerText = heartRate + " BPM";
// Interpretation Logic
var interpText = "";
var interpClass = "";
if (heartRate 100) {
interpText = "Sinus Tachycardia (Fast)";
interpClass = "status-tachy";
} else {
interpText = "Normal Sinus Rhythm";
interpClass = "status-normal";
}
interpDisplay.innerText = interpText;
interpDisplay.className = "interpretation " + interpClass;
// Show container
resultContainer.style.display = 'block';
}
How to Calculate Heart Rate on ECG (25mm/sec)
Interpreting an electrocardiogram (ECG or EKG) is a fundamental skill in cardiology and emergency medicine. While modern ECG machines provide automated readings, understanding how to manually calculate heart rate is crucial for verifying results and detecting artifacts. This guide assumes the standard paper speed of 25 mm/sec.
ECG Grid Basics:
Standard ECG paper typically runs at a speed of 25 mm/second.
• 1 Small Square = 1mm = 0.04 seconds
• 1 Large Square = 5mm = 0.20 seconds
• 5 Large Squares = 1 second
Method 1: The 300 Method (Regular Rhythms)
The "300 Method" is the quickest way to estimate heart rate for regular rhythms. It relies on the fixed time duration of large squares.
The Formula:Heart Rate = 300 ÷ Number of Large Squares between R-R intervals
Why 300? There are 60 seconds in a minute. Since one large square represents 0.20 seconds, the number of large squares in one minute is 60 ÷ 0.20 = 300.
Quick Reference Table:
Large Squares between R-R
Estimated Heart Rate
1
300 BPM
2
150 BPM
3
100 BPM
4
75 BPM
5
60 BPM
6
50 BPM
Method 2: The 1500 Method (Precision)
For a more precise calculation, or when the R-waves do not land exactly on the heavy lines of the large squares, the 1500 method is preferred.
The Formula:Heart Rate = 1500 ÷ Number of Small Squares between R-R intervals
Why 1500? One small square represents 0.04 seconds. The number of small squares in one minute is 60 ÷ 0.04 = 1500.
Example: If there are 20 small squares between two consecutive R waves, the heart rate is 1500 ÷ 20 = 75 BPM.
Method 3: The 6-Second Method (Irregular Rhythms)
When the heart rhythm is irregular (such as in Atrial Fibrillation), the R-R intervals vary, making the 300 and 1500 methods inaccurate. In these cases, you calculate the mean heart rate over a 6-second strip.
How to do it:
Identify a 6-second strip on the ECG paper (this corresponds to 30 large squares).
Count the number of QRS complexes (R waves) that fall within this 6-second period.
Multiply the count by 10 to get the beats per minute.
Example: If you count 8 QRS complexes in 30 large squares, the heart rate is 8 × 10 = 80 BPM.
Interpreting the Results
Once you have calculated the rate, compare it against standard clinical ranges for adults:
Normal Sinus Rhythm: 60 to 100 BPM.
Bradycardia: Less than 60 BPM. Usually indicates a slow heart rhythm.
Tachycardia: Greater than 100 BPM. Indicates a fast heart rhythm.
Note: These calculations apply to adults. Pediatric heart rates have different normal ranges depending on age.