Calculate heart rate based on R-R intervals, small squares, or large squares.
Small Squares Method (1500 Rule)
Large Squares Method (300 Rule)
R-R Interval (Seconds)
25 mm/sec (Standard)
50 mm/sec
Calculated Heart Rate
0 BPM
function updateInputLabel() {
var method = document.getElementById("ecgMethod").value;
var label = document.getElementById("inputLabel");
var input = document.getElementById("ecgInputValue");
if (method === "smallSquares") {
label.innerText = "Number of Small Squares between R waves";
input.placeholder = "e.g. 20";
} else if (method === "largeSquares") {
label.innerText = "Number of Large Squares between R waves";
input.placeholder = "e.g. 4";
} else if (method === "rrInterval") {
label.innerText = "R-R Interval duration (seconds)";
input.placeholder = "e.g. 0.8";
}
}
function calculatePulseRate() {
var method = document.getElementById("ecgMethod").value;
var inputValue = parseFloat(document.getElementById("ecgInputValue").value);
var speed = parseInt(document.getElementById("paperSpeed").value);
var resultBox = document.getElementById("resultBox");
var bpmDisplay = document.getElementById("bpmResult");
var interpDisplay = document.getElementById("bpmInterpretation");
var bpm = 0;
// Validation
if (isNaN(inputValue) || inputValue <= 0) {
alert("Please enter a valid positive number for the measurement.");
return;
}
// Calculation Logic
if (method === "smallSquares") {
// Formula: (Speed * 60) / (Small Squares * 1mm)
// At 25mm/s: (25 * 60) / N = 1500 / N
// At 50mm/s: (50 * 60) / N = 3000 / N
bpm = (speed * 60) / inputValue;
} else if (method === "largeSquares") {
// Formula: (Speed * 60) / (Large Squares * 5mm)
// At 25mm/s: (25 * 60) / (N * 5) = 1500 / 5N = 300 / N
// At 50mm/s: (50 * 60) / (N * 5) = 3000 / 5N = 600 / N
bpm = (speed * 60) / (inputValue * 5);
} else if (method === "rrInterval") {
// Formula: 60 / Time in seconds
bpm = 60 / inputValue;
}
bpm = Math.round(bpm);
// Interpretation
var interpretationText = "";
var interpClass = "";
if (bpm 100) {
interpretationText = "Tachycardia (Fast Heart Rate)";
interpClass = "abnormal-rate";
} else {
interpretationText = "Normal Sinus Rhythm Rate";
interpClass = "normal-rate";
}
// Display Results
bpmDisplay.innerText = bpm + " BPM";
interpDisplay.innerText = interpretationText;
interpDisplay.className = "interpretation " + interpClass;
resultBox.style.display = "block";
}
Understanding ECG Heart Rate Calculation
Calculating the heart rate from an electrocardiogram (ECG or EKG) strip is a fundamental skill for medical professionals, paramedics, and students. The ECG tracks the electrical activity of the heart over time, printed on a grid that allows for precise measurement of time intervals. By measuring the distance between specific waves (usually the R-R interval), we can mathematically determine the heart rate in beats per minute (BPM).
Note on Paper Speed: The standard paper speed for ECGs is 25 mm/sec. However, some clinical settings use 50 mm/sec to visualize detailed waveforms. Always verify the paper speed before calculating, as it changes the constant used in the formulas.
Method 1: The Small Square Method (1500 Rule)
This is the most precise method for calculating heart rates with regular rhythms. The standard ECG paper grid consists of small squares that are 1mm x 1mm. At a standard speed of 25 mm/sec, each small square represents 0.04 seconds.
Formula: 1500 ÷ Number of small squares between two consecutive R waves.
Why 1500? There are 1500 small squares in one minute of ECG strip (25 mm/sec × 60 sec = 1500 mm).
Example: If there are 20 small squares between two R waves: 1500 ÷ 20 = 75 BPM.
Method 2: The Large Square Method (300 Rule)
This method is faster and useful for quick estimations in a clinical setting, though slightly less precise than the small square method. A large square consists of 5 small squares (5mm width). At standard speed, each large square represents 0.20 seconds.
Formula: 300 ÷ Number of large squares between two consecutive R waves.
Why 300? There are 300 large squares in one minute (1500 small squares ÷ 5 = 300).
In modern digital electrophysiology, the heart rate is often calculated using the precise time duration between beats. If you know the time in seconds between two R waves:
Formula: 60 ÷ R-R interval (in seconds).
Example: If the time between beats is 0.8 seconds: 60 ÷ 0.8 = 75 BPM.
Interpreting the Results
Once you have calculated the heart rate, it is categorized clinically:
Normal Sinus Rhythm: 60 to 100 BPM.
Bradycardia: Less than 60 BPM (Slow heart rate).
Tachycardia: Greater than 100 BPM (Fast heart rate).
Note: This calculator assumes a regular rhythm. For irregular rhythms (such as Atrial Fibrillation), the "6-second strip method" (counting QRS complexes in a 6-second period and multiplying by 10) is recommended instead of the R-R interval methods used here.