Calculating Ecg Rate 300

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ECG Heart Rate Calculator (The 300 Method)

Calculate BPM quickly using the R-R interval method

Count the large boxes between two consecutive R-waves.

Use small squares for higher precision (1500 method).

Calculated Heart Rate
—
Beats Per Minute (BPM)

Understanding the “300 Method” in ECG Interpretation

In electrocardiography, the 300 method is a rapid technique used to estimate a patient’s heart rate when the rhythm is regular. This calculation is based on the standard speed of ECG paper, which is 25 mm/sec.

How the Calculation Works

Because there are 300 large squares in one minute of ECG paper moving at standard speed, you can determine the rate by dividing 300 by the number of large squares between two R waves (the R-R interval).

  • 300 ÷ 1 large square = 300 BPM
  • 300 ÷ 2 large squares = 150 BPM
  • 300 ÷ 3 large squares = 100 BPM
  • 300 ÷ 4 large squares = 75 BPM
  • 300 ÷ 5 large squares = 60 BPM
  • 300 ÷ 6 large squares = 50 BPM

When to Use the 1500 Method

For more clinical precision, especially when the R wave does not fall exactly on a heavy line, medical professionals use the 1500 method. Since there are 5 small squares in every large square, there are 1,500 small squares in one minute. The formula is: 1500 / (number of small squares).

Example Calculation

If you observe an ECG strip where there are 3 large squares and 2 small squares between R waves:

  1. Total small squares = (3 × 5) + 2 = 17 small squares.
  2. 1500 ÷ 17 = 88 BPM.
  3. Using the 300 method with decimals: 3.4 large squares. 300 ÷ 3.4 = 88 BPM.
Note: These methods only work for regular rhythms. For irregular rhythms (like Atrial Fibrillation), you should use the “6-second strip method” by counting the number of R waves in a 6-second interval and multiplying by 10.

function calculateECGRate() {
var largeSquares = document.getElementById(“largeSquares”).value;
var smallSquares = document.getElementById(“smallSquares”).value;
var resultDiv = document.getElementById(“ecgResult”);
var bpmDisplay = document.getElementById(“bpmValue”);
var categoryDisplay = document.getElementById(“rhythmCategory”);
var bpm = 0;
// Calculation logic
if (smallSquares && smallSquares > 0) {
// Use 1500 method for precision if small squares are provided
bpm = 1500 / parseFloat(smallSquares);
} else if (largeSquares && largeSquares > 0) {
// Use 300 method
bpm = 300 / parseFloat(largeSquares);
} else {
alert(“Please enter the number of large or small squares.”);
return;
}
var finalBpm = Math.round(bpm);
bpmDisplay.innerHTML = finalBpm;
// Determine Category
var categoryText = “”;
var categoryColor = “”;
var textColor = “#fff”;
if (finalBpm = 60 && finalBpm 100 && finalBpm <= 150) {
categoryText = "Tachycardia";
categoryColor = "#f57c00"; // Orange
} else {
categoryText = "Extreme Tachycardia / SVT";
categoryColor = "#d32f2f"; // Red
}
categoryDisplay.innerHTML = categoryText;
categoryDisplay.style.backgroundColor = categoryColor;
categoryDisplay.style.color = textColor;
resultDiv.style.display = "block";
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}

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