Small Squares Method (1500 Rule)
Large Squares Method (300 Rule)
Time Interval (Seconds)
Uses the count of small boxes (1mm) between R-R intervals. Most precise.
Count the number of 1mm boxes between two consecutive R-waves.
Estimated Heart Rate
0
Beats Per Minute
Formula to Calculate Heart Rate from ECG
Calculating heart rate from an Electrocardiogram (ECG or EKG) strip is a fundamental skill for healthcare professionals. While modern ECG machines provide automated readings, understanding the manual calculation formulas is crucial for verifying results and interpreting rhythms where the machine might err. This calculator uses standard ECG paper settings (25 mm/sec) to determine the rate based on the R-R interval.
The Standard ECG Grid
To use the formulas correctly, one must understand the standard calibration of ECG paper:
Paper Speed: Standard speed is 25 mm/sec.
Small Square (1mm): Represents 0.04 seconds horizontally.
Large Square (5mm): Consists of 5 small squares and represents 0.20 seconds horizontally.
Method 1: The 1500 Method (Small Squares)
This is the most precise method for calculating heart rate for regular rhythms. Because there are 1500 small squares in one minute (25 mm/sec × 60 sec = 1500 mm), you can determine the heart rate by dividing 1500 by the number of small squares between two R-waves.
Heart Rate (BPM) = 1500 ÷ Number of Small Squares between R-R
Example: If there are 20 small squares between two R-waves: 1500 ÷ 20 = 75 BPM.
Method 2: The 300 Method (Large Squares)
This method is faster but slightly less precise, often used for quick visual estimation. Since there are 300 large squares in a minute (300 ÷ 0.20s = 1500 small squares), the formula involves dividing 300 by the number of large squares.
Heart Rate (BPM) = 300 ÷ Number of Large Squares between R-R
Sequence to memorize: 300, 150, 100, 75, 60, 50. (e.g., 1 large square = 300 bpm, 2 large squares = 150 bpm, etc.)
Method 3: Time Interval
If you have the exact time measurement of the R-R interval in seconds (often provided by digital calipers or electrophysiology software), the calculation is straightforward physics.
Heart Rate (BPM) = 60 ÷ R-R Interval (in seconds)
Interpreting the Results
For a standard adult resting heart rate:
Normal Sinus Rhythm: 60 to 100 BPM.
Sinus Bradycardia: Less than 60 BPM (slow heart rate).
Sinus Tachycardia: More than 100 BPM (fast heart rate).
When to use these formulas?
These formulas are accurate for regular rhythms (where the distance between R-waves is consistent). For irregular rhythms (like Atrial Fibrillation), the "6-Second Method" is preferred, which involves counting the number of QRS complexes in a 6-second strip and multiplying by 10.
Disclaimer: This calculator is for educational and informational purposes only. It is not a medical device and should not be used for diagnosis or treatment. Always consult with a qualified healthcare professional for medical advice and ECG interpretation.
function updateLabels() {
var method = document.getElementById('calcMethod').value;
var label = document.getElementById('inputLabel');
var helper = document.getElementById('methodHelper');
var inputHelper = document.getElementById('inputHelper');
var inputField = document.getElementById('rrInput');
inputField.value = "; // Clear input on switch
document.getElementById('resultOutput').style.display = 'none';
if (method === '1500') {
label.innerText = 'Number of Small Squares';
helper.innerText = 'Uses the count of small boxes (1mm) between R-R intervals. Most precise.';
inputHelper.innerText = 'Count the small 1mm boxes between two R-waves.';
inputField.placeholder = 'e.g., 20';
} else if (method === '300') {
label.innerText = 'Number of Large Squares';
helper.innerText = 'Uses the count of large boxes (5mm) between R-R intervals. Quick estimation.';
inputHelper.innerText = 'Count the large 5mm boxes between two R-waves.';
inputField.placeholder = 'e.g., 4';
} else if (method === 'time') {
label.innerText = 'R-R Interval (Seconds)';
helper.innerText = 'Uses the exact time duration between R-waves.';
inputHelper.innerText = 'Enter the time in seconds (e.g., 0.8).';
inputField.placeholder = 'e.g., 0.8';
}
}
function calculateHeartRate() {
var method = document.getElementById('calcMethod').value;
var inputValue = parseFloat(document.getElementById('rrInput').value);
var resultDiv = document.getElementById('resultOutput');
var bpmDisplay = document.getElementById('bpmDisplay');
var statusDisplay = document.getElementById('statusDisplay');
// Validation
if (isNaN(inputValue) || inputValue <= 0) {
alert("Please enter a valid positive number.");
return;
}
var heartRate = 0;
// Logic based on Method
if (method === '1500') {
// Formula: 1500 / small squares
heartRate = 1500 / inputValue;
} else if (method === '300') {
// Formula: 300 / large squares
heartRate = 300 / inputValue;
} else if (method === 'time') {
// Formula: 60 / seconds
heartRate = 60 / inputValue;
}
// Round to nearest integer for clinical relevance
var roundedHR = Math.round(heartRate);
// Interpretation Logic
var statusText = "";
var statusClass = "";
if (roundedHR = 60 && roundedHR <= 100) {
statusText = "Normal Resting Rate";
statusClass = "status-normal";
} else {
statusText = "Tachycardia (Fast)";
statusClass = "status-danger";
}
// Display Results
bpmDisplay.innerText = roundedHR;
statusDisplay.innerText = statusText;
// Remove old classes and add new one
statusDisplay.classList.remove('status-normal', 'status-warning', 'status-danger');
statusDisplay.classList.add(statusClass);
resultDiv.style.display = 'block';
}