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Ways to Calculate Heart Rate on ECG
Calculating the heart rate from an electrocardiogram (ECG or EKG) is a fundamental skill for healthcare professionals, students, and paramedics. An accurate determination of heart rate is the first step in interpreting cardiac rhythms, identifying arrhythmias, and determining patient stability. While modern ECG machines provide automated readouts, manual verification remains essential to avoid computer interpretation errors.
This guide details the standard methods for calculating heart rate assuming a standard paper speed of 25 mm/second.
1. The 1500 Method (The Most Precise)
The 1500 method is considered the most accurate way to calculate heart rate for regular rhythms. It relies on the small squares on the ECG paper (1mm x 1mm). Since the paper speed is 25mm/second, there are 1,500 small squares in one minute (25 mm/sec x 60 sec = 1500 mm/min).
Heart Rate = 1500 ÷ Number of Small Squares between R-R
How to use it:
- Identify two consecutive R waves (the peaks of the QRS complex).
- Count the number of small (1mm) boxes between them.
- Divide 1500 by this number.
Example: If there are 20 small squares between R waves, the heart rate is 1500 ÷ 20 = 75 BPM.
2. The 300 Method (The Sequence Method)
The 300 method is a quicker estimation tool, ideal for rapid assessment of regular rhythms. It uses the large squares (5mm x 5mm). There are 300 large squares in one minute (1500 small squares ÷ 5 small squares per large square = 300).
Heart Rate = 300 ÷ Number of Large Squares between R-R
Memorization Sequence:
You can also memorize the sequence for consecutive large lines following an R wave: 300, 150, 100, 75, 60, 50, 43, 37.
- 1 large square = 300 BPM
- 2 large squares = 150 BPM
- 3 large squares = 100 BPM
- 4 large squares = 75 BPM
3. The 6-Second Method (For Irregular Rhythms)
When a patient has an irregular rhythm, such as Atrial Fibrillation (A-Fib), the R-R intervals vary significantly. In these cases, the 1500 and 300 methods will be inaccurate. The 6-second method provides a mean heart rate.
Heart Rate = Number of QRS complexes in 6 seconds x 10
How to use it:
- Obtain a 6-second strip of the ECG. On standard paper, this is equal to 30 large squares.
- Count the number of complete QRS complexes within that 6-second window.
- Multiply that count by 10 to get the beats per minute.
Example: If you count 8 QRS complexes in a 6-second strip, the heart rate is 8 x 10 = 80 BPM.
Clinical Interpretation of Heart Rate
Once you have calculated the heart rate, you categorize the rhythm based on the resting rate of the adult patient:
- Bradycardia: Heart Rate < 60 BPM. Can be normal in athletes or during sleep, but may indicate pathology in others.
- Normal Sinus Rhythm: Heart Rate 60 – 100 BPM.
- Tachycardia: Heart Rate > 100 BPM. Can be caused by stress, exercise, fever, or cardiac arrhythmias.
function toggleInputs() {
var method = document.getElementById('methodSelect').value;
// Hide all sections
document.getElementById('input1500').style.display = 'none';
document.getElementById('input300').style.display = 'none';
document.getElementById('input6sec').style.display = 'none';
document.getElementById('inputRR').style.display = 'none';
// Hide result
document.getElementById('resultDisplay').style.display = 'none';
// Show specific section
if (method === '1500') {
document.getElementById('input1500').style.display = 'block';
} else if (method === '300') {
document.getElementById('input300').style.display = 'block';
} else if (method === '6sec') {
document.getElementById('input6sec').style.display = 'block';
} else if (method === 'rr') {
document.getElementById('inputRR').style.display = 'block';
}
}
function calculateECG() {
var method = document.getElementById('methodSelect').value;
var bpm = 0;
var isValid = false;
if (method === '1500') {
var smallBoxes = parseFloat(document.getElementById('smallSquares').value);
if (!isNaN(smallBoxes) && smallBoxes > 0) {
bpm = 1500 / smallBoxes;
isValid = true;
}
} else if (method === '300') {
var largeBoxes = parseFloat(document.getElementById('largeSquares').value);
if (!isNaN(largeBoxes) && largeBoxes > 0) {
bpm = 300 / largeBoxes;
isValid = true;
}
} else if (method === '6sec') {
var qrs = parseFloat(document.getElementById('qrsCount').value);
if (!isNaN(qrs) && qrs >= 0) {
bpm = qrs * 10;
isValid = true;
}
} else if (method === 'rr') {
var rrSec = parseFloat(document.getElementById('rrInterval').value);
if (!isNaN(rrSec) && rrSec > 0) {
bpm = 60 / rrSec;
isValid = true;
}
}
var resultBox = document.getElementById('resultDisplay');
var bpmValue = document.getElementById('bpmValue');
var bpmStatus = document.getElementById('bpmStatus');
if (isValid) {
var finalBPM = Math.round(bpm);
resultBox.style.display = 'block';
bpmValue.innerHTML = finalBPM + '
';
// Determine clinical status
bpmStatus.className = 'status-badge'; // reset
if (finalBPM 100) {
bpmStatus.innerHTML = "Tachycardia";
bpmStatus.classList.add('status-tachy');
} else {
bpmStatus.innerHTML = "Normal Rate";
bpmStatus.classList.add('status-normal');
}
} else {
alert("Please enter a valid positive number for the selected method.");
resultBox.style.display = 'none';
}
}