Count the smallest boxes (1mm) between two consecutive R waves.
Count the heavy-line boxes (5mm) between two consecutive R waves.
Count all R waves visible in a 30-large-square strip.
The exact time in seconds between two R waves.
Estimated Heart Rate
0 BPM
function toggleInputs() {
var method = document.getElementById('calculationMethod').value;
// Hide all inputs first
document.getElementById('input-1500').style.display = 'none';
document.getElementById('input-300').style.display = 'none';
document.getElementById('input-6sec').style.display = 'none';
document.getElementById('input-rr_time').style.display = 'none';
document.getElementById('resultOutput').style.display = 'none';
// Show relevant input
if (method === '1500') {
document.getElementById('input-1500').style.display = 'block';
} else if (method === '300') {
document.getElementById('input-300').style.display = 'block';
} else if (method === '6sec') {
document.getElementById('input-6sec').style.display = 'block';
} else if (method === 'rr_time') {
document.getElementById('input-rr_time').style.display = 'block';
}
}
function calculateECG() {
var method = document.getElementById('calculationMethod').value;
var rate = 0;
var isValid = false;
var note = "";
if (method === '1500') {
var smallSq = parseFloat(document.getElementById('smallSquares').value);
if (smallSq > 0) {
rate = 1500 / smallSq;
isValid = true;
note = "Calculation: 1500 / " + smallSq + " small squares";
}
} else if (method === '300') {
var largeSq = parseFloat(document.getElementById('largeSquares').value);
if (largeSq > 0) {
rate = 300 / largeSq;
isValid = true;
note = "Calculation: 300 / " + largeSq + " large squares";
}
} else if (method === '6sec') {
var qrs = parseFloat(document.getElementById('qrsCount').value);
if (qrs >= 0) {
rate = qrs * 10;
isValid = true;
note = "Calculation: " + qrs + " complexes × 10″;
}
} else if (method === 'rr_time') {
var sec = parseFloat(document.getElementById('rrSeconds').value);
if (sec > 0) {
rate = 60 / sec;
isValid = true;
note = "Calculation: 60 / " + sec + " seconds";
}
}
var resultBox = document.getElementById('resultOutput');
if (isValid) {
resultBox.style.display = 'block';
var finalRate = Math.round(rate);
document.getElementById('bpmValue').innerHTML = finalRate + " BPM";
document.getElementById('methodNote').innerText = note;
var statusDiv = document.getElementById('rhythmStatus');
statusDiv.className = 'status-display'; // reset classes
if (finalRate 100) {
statusDiv.innerText = "Tachycardia (Fast Heart Rate)";
statusDiv.classList.add('status-tachy');
} else {
statusDiv.innerText = "Normal Resting Heart Rate";
statusDiv.classList.add('status-normal');
}
} else {
alert("Please enter a valid positive number for the selected method.");
}
}
How to Calculate Rate in ECG Strips: A Complete Guide
Interpreting an Electrocardiogram (ECG/EKG) is a fundamental skill for medical professionals. The first and often most critical step in interpretation is calculating the heart rate. The heart rate determines whether a patient is bradycardic, tachycardic, or within a normal range, which dictates immediate clinical decisions.
There are several methods to calculate heart rate from an ECG strip, depending on the regularity of the rhythm and the precision required. This calculator employs the four most standard techniques used in cardiology.
Understanding the ECG Grid
Before calculating the rate, it is essential to understand the calibration of standard ECG paper:
Paper Speed: Standard paper speed is 25 mm/second.
Small Squares: Each small box is 1mm x 1mm and represents 0.04 seconds.
Large Squares: Each large box consists of 5 small squares (5mm x 5mm) and represents 0.20 seconds.
Time Markers: Often, there are hash marks at the top or bottom of the paper indicating 3-second intervals.
Method 1: The 1500 Method (Small Squares)
The 1500 method is the most precise technique for calculating heart rate, provided the rhythm is regular (the distance between R waves is consistent).
Formula: 1500 ÷ Number of Small Squares between R-R intervals.
Why 1500? There are 1,500 small (1mm) squares in one minute of an ECG trace running at 25mm/s (25mm/s × 60s = 1500mm).
Method 2: The 300 Method (Large Squares)
The 300 method is a quick estimation tool, ideal for rapid assessment in emergency situations. It is essentially a simplified version of the 1500 method.
Formula: 300 ÷ Number of Large Squares between R-R intervals.
Sequence Memory: Many clinicians memorize the sequence for large boxes: 300, 150, 100, 75, 60, 50. If the R-R interval is 1 box, the rate is 300 bpm; if 2 boxes, 150 bpm, and so on.
Method 3: The 6-Second Strip Method
While the square counting methods work well for regular rhythms, they are inaccurate for irregular rhythms like Atrial Fibrillation. In these cases, the 6-second method provides an average rate.
How to do it:
Identify a 6-second section on the ECG paper (usually marked by 3 hash marks at the top, representing 30 large squares).
Count the number of QRS complexes (R waves) within that 6-second window.
Multiply the count by 10 to get the beats per minute (6 seconds × 10 = 60 seconds).
Method 4: Digital Interval Method
With modern digital calipers or electrophysiology software, you may measure the exact time in seconds between beats. This is highly accurate.
Formula: 60 ÷ R-R Interval in Seconds.
Clinical Interpretations
Normal Sinus Rhythm: 60 – 100 BPM
Sinus Bradycardia: Less than 60 BPM
Sinus Tachycardia: Greater than 100 BPM
Always verify your calculation by checking the patient's pulse physically, especially if the ECG waveform is prone to artifact or interference.