Large Square Method (Regular Rhythm)
Small Square Method (High Precision)
6-Second Method (Irregular Rhythm)
function updateLabels() {
var method = document.getElementById("ecgMethod").value;
var label = document.getElementById("ecgValLabel");
var input = document.getElementById("ecgValue");
if (method === "large") {
label.innerText = "Number of Large Squares (R-R Interval)";
input.placeholder = "e.g. 4";
} else if (method === "small") {
label.innerText = "Number of Small Squares (R-R Interval)";
input.placeholder = "e.g. 20";
} else if (method === "6second") {
label.innerText = "Number of QRS Complexes in 6 Seconds";
input.placeholder = "e.g. 7";
}
}
function calculateECG() {
var method = document.getElementById("ecgMethod").value;
var val = parseFloat(document.getElementById("ecgValue").value);
var resDiv = document.getElementById("ecgResult");
var hrDisplay = document.getElementById("hrDisplay");
var hrCat = document.getElementById("hrCategory");
if (isNaN(val) || val <= 0) {
alert("Please enter a valid positive number.");
return;
}
var hr = 0;
if (method === "large") {
hr = 300 / val;
} else if (method === "small") {
hr = 1500 / val;
} else if (method === "6second") {
hr = val * 10;
}
var roundedHR = Math.round(hr);
hrDisplay.innerHTML = "Calculated Heart Rate: " + roundedHR + " BPM";
var category = "";
var color = "";
if (roundedHR 100) {
category = "Tachycardia (Fast Heart Rate)";
color = "#ff9800";
} else {
category = "Normal Sinus Rhythm";
color = "#4caf50";
}
hrCat.innerText = category;
hrCat.style.color = color;
resDiv.style.display = "block";
}
How to Calculate Heart Rate from an ECG Tracing
Electrocardiogram (ECG) interpretation is a fundamental skill in clinical medicine. Determining the heart rate (HR) accurately is the first step in rhythm analysis. This guide covers the three primary methods used by healthcare professionals to calculate heart rate from standard ECG paper.
Standard ECG Paper Basics
Before calculating, you must understand the grid system on standard ECG paper (running at 25 mm/sec):
Small Square: 1mm x 1mm = 0.04 seconds.
Large Square: 5mm x 5mm (5 small squares) = 0.20 seconds.
5 Large Squares: 1 second.
30 Large Squares: 6 seconds.
Method 1: The Large Square Method (300 Method)
This is the most popular "quick look" method for regular rhythms. To use this, count the number of large squares between two consecutive R-waves (the R-R interval).
Formula:HR = 300 / (Number of Large Squares)
Example: If there are 4 large squares between R-waves, the heart rate is 300 / 4 = 75 BPM.
Method 2: The Small Square Method (1500 Method)
This method provides the highest level of accuracy for regular rhythms. Instead of large squares, count the total number of small squares between two R-waves.
Formula:HR = 1500 / (Number of Small Squares)
Example: If there are 20 small squares between R-waves, the heart rate is 1500 / 20 = 75 BPM.
Method 3: The 6-Second Method
This is the preferred method for irregular rhythms (like Atrial Fibrillation). Because the distance between R-waves varies, you must average the rate over time.
Identify a 6-second strip (30 large squares).
Count the number of QRS complexes (R-waves) within that 6-second period.
Multiply that count by 10.
Formula:HR = (Number of QRS complexes in 6s) x 10
ECG Measurement Reference Table
R-R Interval (Large Squares)
Heart Rate (BPM)
Classification
1 Square
300
Extreme Tachycardia
2 Squares
150
Tachycardia
3 Squares
100
Normal Limit (Upper)
4 Squares
75
Normal
5 Squares
60
Normal Limit (Lower)
6 Squares
50
Bradycardia
Clinical Significance
Identifying the heart rate is critical for diagnosing conditions like Bradycardia (HR < 60 BPM) or Tachycardia (HR > 100 BPM). Always ensure the ECG paper speed is set to the standard 25 mm/s; if the paper speed is 50 mm/s, these formulas must be doubled.