body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
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.calculator-container {
background-color: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
margin-bottom: 40px;
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font-weight: bold;
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margin-top: 25px;
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.result-value {
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function updateInputLabels() {
var method = document.getElementById('calcMethod').value;
var label = document.getElementById('dynamicInputLabel');
var input = document.getElementById('ecgInputValue');
if (method === '1500') {
label.innerText = "Number of Small Squares between R-R Waves";
input.placeholder = "e.g., 20";
} else if (method === '300') {
label.innerText = "Number of Large Squares between R-R Waves";
input.placeholder = "e.g., 4";
} else if (method === '6sec') {
label.innerText = "Number of QRS Complexes in 6 Seconds";
input.placeholder = "e.g., 8";
}
}
function calculateHeartRate() {
var speed = parseFloat(document.getElementById('paperSpeed').value);
var method = document.getElementById('calcMethod').value;
var inputValue = parseFloat(document.getElementById('ecgInputValue').value);
var resultBox = document.getElementById('resultBox');
var bpmDisplay = document.getElementById('bpmResult');
var interpretation = document.getElementById('interpretation');
if (isNaN(inputValue) || inputValue <= 0) {
alert("Please enter a valid positive number.");
return;
}
var heartRate = 0;
var formulaText = "";
// Standard calculation constants
// At 25mm/s, 1 min = 1500 small squares (25 * 60)
// At 50mm/s, 1 min = 3000 small squares (50 * 60)
var minuteInMm = speed * 60; // 1500 or 3000
if (method === '1500') {
// Formula: (Speed * 60) / Small Squares
heartRate = minuteInMm / inputValue;
} else if (method === '300') {
// Formula: ((Speed * 60) / 5) / Large Squares
// At 25mm/s: 300 / Large Squares
// At 50mm/s: 600 / Large Squares
var numerator = minuteInMm / 5;
heartRate = numerator / inputValue;
} else if (method === '6sec') {
// Formula: Count * 10
// This method assumes the strip is exactly 6 seconds long regardless of paper speed logic for counting
heartRate = inputValue * 10;
}
heartRate = Math.round(heartRate);
// Interpretation
var interpText = "";
if (heartRate 100) {
interpText = "Indicates Tachycardia (Fast Heart Rate)";
} else {
interpText = "Normal Resting Heart Rate Range";
}
bpmDisplay.innerText = heartRate + " BPM";
interpretation.innerText = interpText;
resultBox.style.display = "block";
}
How to Calculate Heart Rate from ECG Paper
Interpreting an Electrocardiogram (ECG or EKG) is a fundamental skill for medical professionals. While modern ECG machines provide automated readouts, understanding how to calculate heart rate manually from the ECG paper is crucial for verifying results, diagnosing equipment errors, and interpreting rhythm strips in emergency situations.
This guide breaks down the mathematics behind ECG paper grids and explains the three standard methods for calculating heart rate: the 1500 method, the 300 method, and the 6-second method.
Understanding the ECG Grid
Before calculating the rate, you must understand the standard calibration of ECG paper. The paper records time horizontally and voltage vertically.
Standard Calibration (25 mm/sec):
- Small Square (1mm): Represents 0.04 seconds.
- Large Square (5mm): Composed of 5 small squares. Represents 0.20 seconds.
- 1 Second: Equals 5 large squares or 25 small squares.
- 1 Minute: Equals 300 large squares or 1500 small squares.
Method 1: The 1500 Method (Small Squares)
The 1500 method is the most precise way to calculate heart rate for regular rhythms. It relies on counting the exact number of small (1mm) squares between two consecutive R waves (the peak of the QRS complex).
The Formula
Heart Rate = 1500 / Number of Small Squares
This constant (1500) is derived from the fact that at a standard paper speed of 25 mm/s, there are 1500 small squares in one minute (25 mm/sec × 60 sec/min).
Example: If there are 20 small squares between two R waves:
1500 ÷ 20 = 75 BPM.
Method 2: The 300 Method (Large Squares)
The 300 method, also known as the sequence method, is a quick way to estimate heart rate without counting tiny grid lines. It is ideal for rapid assessment of regular rhythms.
The Formula
Heart Rate = 300 / Number of Large Squares
There are 300 large squares in one minute (1500 small squares ÷ 5). To use this method, find an R wave that falls on a thick line, then count the number of large squares to the next R wave.
Quick Reference Sequence:
- 1 large square = 300 BPM
- 2 large squares = 150 BPM
- 3 large squares = 100 BPM
- 4 large squares = 75 BPM
- 5 large squares = 60 BPM
- 6 large squares = 50 BPM
Method 3: The 6-Second Method (Irregular Rhythms)
When the heart rhythm is irregular (such as in Atrial Fibrillation), the distance between R waves varies, making the 1500 and 300 methods inaccurate. In these cases, the 6-second method is the standard approach.
How to Perform It
- Identify a 6-second strip on the ECG paper. At 25 mm/s, this equals 30 large squares. Standard ECG paper often has hash marks at the top or bottom indicating 3-second intervals.
- Count the number of complete QRS complexes (R waves) within that 6-second interval.
- Multiply the count by 10 to get the beats per minute.
Example: If you count 8 QRS complexes in a 6-second strip:
8 × 10 = 80 BPM.
Adjusting for Paper Speed
While 25 mm/sec is the standard, some clinical settings use 50 mm/sec to examine waveforms in greater detail. If the paper speed is 50 mm/sec, the math changes:
- 1500 Method becomes the 3000 Method: HR = 3000 / Small Squares.
- 300 Method becomes the 600 Method: HR = 600 / Large Squares.
Our calculator above automatically adjusts for these speed settings to ensure accuracy.