Count the small 1mm squares between two consecutive R peaks.
Calculated Heart Rate:
function updateLabels() {
var method = document.getElementById("calcMethod").value;
var label = document.getElementById("inputLabel");
var help = document.getElementById("helpText");
var input = document.getElementById("inputValue");
if (method === "1500") {
label.innerText = "Number of Small Squares (R-R interval):";
help.innerText = "Count the tiny 1mm squares between two R waves. Most accurate for regular rhythms.";
input.placeholder = "e.g., 20";
} else if (method === "300") {
label.innerText = "Number of Large Squares (R-R interval):";
help.innerText = "Count the 5mm boxes between two R waves.";
input.placeholder = "e.g., 4";
} else {
label.innerText = "Number of QRS Complexes (in a 6-second strip):";
help.innerText = "Count how many R-waves appear in a 30-large-square section (6 seconds). Best for irregular rhythms.";
input.placeholder = "e.g., 8";
}
}
function calculateECG() {
var method = document.getElementById("calcMethod").value;
var val = parseFloat(document.getElementById("inputValue").value);
var resultDiv = document.getElementById("ecgResult");
var bpmOutput = document.getElementById("bpmOutput");
var classOutput = document.getElementById("classification");
var bpm = 0;
if (isNaN(val) || val <= 0) {
alert("Please enter a valid positive number.");
return;
}
if (method === "1500") {
bpm = 1500 / val;
} else if (method === "300") {
bpm = 300 / val;
} else {
bpm = val * 10;
}
var roundedBpm = Math.round(bpm);
bpmOutput.innerText = roundedBpm + " BPM";
var status = "";
var color = "";
if (roundedBpm 100) {
status = "Tachycardia (Fast)";
color = "#f44336";
} else {
status = "Normal Sinus Rhythm";
color = "#4CAF50";
}
classOutput.innerText = status;
classOutput.style.color = color;
resultDiv.style.display = "block";
resultDiv.style.backgroundColor = "#fef2f2";
resultDiv.style.border = "1px solid #fee2e2";
}
How to Calculate Heart Rate on an ECG Strip
Electrocardiogram (ECG) interpretation requires speed and accuracy. Determining the heart rate (beats per minute) is one of the first steps in clinical rhythm analysis. Depending on whether the rhythm is regular or irregular, different mathematical constants are used.
1. The 1500 Method (Most Accurate)
The 1500 method is used for regular rhythms. ECG paper usually moves at a standard speed of 25 mm/sec. This means there are 1,500 small squares (1mm each) in one minute of recording.
Formula: 1500 / (Number of small squares between two R waves)
Example: If there are 20 small squares between R waves: 1500 / 20 = 75 BPM.
2. The 300 Method (Large Square Method)
The 300 method is a quicker version of the 1500 method. Since one large square contains 5 small squares, there are 300 large squares in one minute (1500 / 5 = 300).
Formula: 300 / (Number of large squares between two R waves)
Example: If there are 4 large squares: 300 / 4 = 75 BPM.
3. The 6-Second Method (For Irregular Rhythms)
When a patient has an irregular rhythm (like Atrial Fibrillation), the distance between R-waves varies. In these cases, we count the number of QRS complexes in a set timeframe.
Formula: (Number of R-waves in 6 seconds) × 10
Tip: Most ECG strips have markers at 3-second intervals. Count the complexes across two of these intervals (6 seconds total).
Normal Heart Rate Ranges
Classification
Range (BPM)
Bradycardia
Less than 60
Normal Rhythm
60 – 100
Tachycardia
Greater than 100
Disclaimer: This calculator is for educational purposes only. Always consult with a qualified medical professional for clinical diagnosis and interpretation of ECG results.