Heart Rate Calculation by Ecg

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ECG Heart Rate Calculator

Quickly determine heart rate (BPM) based on the R-R interval squares on an EKG tracing.

Large Square Method (300 Rule) Small Square Method (1500 Rule)
Count the large boxes between two consecutive R peaks.
Count the tiny 1mm boxes between two consecutive R peaks for higher precision.
function toggleInputs() { var method = document.getElementById("calcMethod").value; var largeGroup = document.getElementById("largeInputGroup"); var smallGroup = document.getElementById("smallInputGroup"); if (method === "large") { largeGroup.style.display = "block"; smallGroup.style.display = "none"; } else { largeGroup.style.display = "none"; smallGroup.style.display = "block"; } } function calculateECG() { var method = document.getElementById("calcMethod").value; var bpm = 0; var resultDiv = document.getElementById("ecgResult"); var hrValueDiv = document.getElementById("hrValue"); var hrStatusDiv = document.getElementById("hrStatus"); if (method === "large") { var squares = parseFloat(document.getElementById("largeSquares").value); if (squares > 0) { bpm = 300 / squares; } } else { var squares = parseFloat(document.getElementById("smallSquares").value); if (squares > 0) { bpm = 1500 / squares; } } if (bpm > 0) { var finalBpm = Math.round(bpm); hrValueDiv.innerHTML = finalBpm + " BPM"; resultDiv.style.display = "block"; resultDiv.style.backgroundColor = "#fff5f5"; var status = ""; var color = ""; if (finalBpm 100) { status = "Tachycardia (Fast Heart Rate)"; color = "#e67e22"; } else { status = "Normal Sinus Rhythm"; color = "#27ae60"; } hrStatusDiv.innerHTML = status; hrStatusDiv.style.color = color; } else { alert("Please enter a valid number of squares."); } }

How to Calculate Heart Rate from an ECG Tracing

Electrocardiogram (ECG/EKG) interpretation is a fundamental skill in clinical medicine. One of the first steps in analyzing a rhythm strip is determining the heart rate. This calculator utilizes the two most common mathematical methods used by healthcare professionals when dealing with regular heart rhythms.

1. The Large Square Method (The 300 Rule)

Standard ECG paper moves at a speed of 25 mm/s. On this paper, one large square represents 0.2 seconds. Since there are 300 large squares in a minute (60 seconds / 0.2), you can find the heart rate by dividing 300 by the number of large squares between two consecutive R waves (the R-R interval).

  • Formula: HR = 300 / Number of Large Squares
  • Example: If there are 4 large squares between R waves, 300 / 4 = 75 BPM.

2. The Small Square Method (The 1500 Rule)

For a more precise measurement, especially when the R waves don't land exactly on the heavy grid lines, the small square method is preferred. One small square represents 0.04 seconds. There are 1,500 small squares in one minute.

  • Formula: HR = 1500 / Number of Small Squares
  • Example: If there are 22 small squares between R waves, 1500 / 22 = 68 BPM.

Standard Heart Rate Classifications

Once you have calculated the heart rate, it is typically categorized as follows for a resting adult:

Category Rate (BPM)
Bradycardia Less than 60
Normal Rhythm 60 – 100
Tachycardia Greater than 100

Important Consideration: Irregular Rhythms

Note that the methods above (300 and 1500 rules) only work for regular rhythms. If the spacing between R waves varies (as seen in Atrial Fibrillation), you should use the 6-second method: count the number of R waves in a 6-second strip (30 large squares) and multiply that number by 10.

Disclaimer: This calculator is for educational purposes only. Clinical decisions should always be made by qualified medical professionals interpreting a full diagnostic ECG in the context of the patient's clinical presentation.

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