6 Seconds (30 large squares)
10 Seconds (50 large squares)
3 Seconds (15 large squares)
Estimated Heart Rate0Beats Per Minute (BPM)
Method: (QRS Count / Strip Duration) × 60
function calculateECGHeartRate() {
var qrs = document.getElementById("qrsCount").value;
var seconds = document.getElementById("stripLength").value;
var resultDiv = document.getElementById("ecgResult");
var bpmOutput = document.getElementById("bpmOutput");
var interpretation = document.getElementById("interpretation");
if (qrs === "" || qrs <= 0) {
alert("Please enter a valid number of QRS complexes.");
return;
}
var qrsNum = parseFloat(qrs);
var secNum = parseFloat(seconds);
// Formula: (Number of complexes / seconds) * 60 seconds
var bpm = Math.round((qrsNum / secNum) * 60);
bpmOutput.innerHTML = bpm;
resultDiv.style.display = "block";
var message = "";
if (bpm = 60 && bpm <= 100) {
message = "Interpretation: This is within the Normal resting heart rate range.";
} else {
message = "Interpretation: This indicates Tachycardia (Fast heart rate).";
}
interpretation.innerHTML = message;
}
How to Calculate Heart Rate from ECG with Irregular Rhythm
In clinical practice, determining the heart rate from an Electrocardiogram (ECG) is straightforward when the rhythm is regular. However, when a patient presents with an irregular rhythm—such as Atrial Fibrillation (AFib) or frequent premature contractions—traditional methods like the "300 Rule" or the "1500 Rule" become inaccurate. For irregular rhythms, the 6-Second Method is the gold standard.
Why Regular Methods Fail
The 1500 rule (1500 divided by the number of small squares between two R-waves) assumes that the distance between all R-waves is identical. In an irregular rhythm, the R-R interval varies significantly from beat to beat. If you calculate based on one short interval, you may overestimate the rate; if you use a long interval, you underestimate it.
The 6-Second Strip Method
The most reliable way to calculate an irregular heart rate is to look at a longer period of time to find the average. The standard ECG paper speed is 25 mm/sec. This means:
1 small square = 0.04 seconds.
1 large square (5 small squares) = 0.20 seconds.
30 large squares = 6 seconds.
By counting the number of R-waves in a 6-second window and multiplying by 10, you obtain the average beats per minute (BPM).
Step-by-Step Calculation
Identify the 6-second window: Locate 30 large squares on the ECG rhythm strip. Most ECG paper has small hash marks at the top or bottom indicating 3-second intervals.
Count the QRS complexes: Count every R-wave (the tall spikes) within that 30-square boundary.
Apply the Math: Multiply the number of complexes by 10. (e.g., 8 complexes × 10 = 80 BPM).
Example Scenarios
QRS Count (6 sec)
Calculation
Resulting HR
7
7 x 10
70 BPM
12
12 x 10
120 BPM
5
5 x 10
50 BPM
Clinical Pearl
If the rhythm is extremely irregular, some practitioners prefer using a 10-second strip (50 large squares) and multiplying by 6 for even greater accuracy. This minimizes the impact of a single "extra" beat on the final calculation.