How to Calculate Heart Rate from Ecg

ECG Heart Rate Calculator

Understanding How to Calculate Heart Rate from an ECG

Electrocardiograms (ECGs or EKGs) are vital diagnostic tools that record the electrical activity of the heart. One of the most fundamental pieces of information derived from an ECG is the heart rate. Calculating the heart rate from an ECG strip allows healthcare professionals to assess whether the heart is beating too fast (tachycardia), too slow (bradycardia), or at a normal rhythm. There are several methods to calculate heart rate from an ECG, each suited to different situations and the quality of the ECG recording.

Methods for Calculating Heart Rate from an ECG:

1. Using the RR Interval: The most accurate method involves measuring the time between two consecutive R-waves (the tallest peak in the QRS complex), known as the RR interval.
   • If you know the RR interval in seconds, the heart rate (in beats per minute, bpm) can be calculated using the formula: Heart Rate = 60 / RR Interval (in seconds)
   • This calculator also provides methods that use measurements from the ECG paper itself.
2. Using the Number of Large Boxes: ECG paper is gridded with small boxes (typically 1mm) and large boxes (5mm, or 0.2 seconds at a standard paper speed of 25 mm/sec).
   • If the rhythm is regular, you can count the number of large boxes between two consecutive R-waves and use the formula: Heart Rate = 300 / Number of Large Boxes Between R-waves
3. Using Small Boxes: For more precise calculations or when the rhythm is slightly irregular, you can count the number of small boxes between two consecutive R-waves.
   • The formula is: Heart Rate = 1500 / Number of Small Boxes Between R-waves
   • This calculator can derive the number of small boxes from the RR interval in seconds and the standard small box duration (0.04 seconds).
4. Using ECG Paper Speed: The paper speed of the ECG machine (usually 25 mm/sec) is crucial for converting distances on the ECG strip into time.
   • The duration of a small box in seconds is 1mm / paper speed (e.g., 1mm / 25mm/sec = 0.04 sec).
   • The duration of a large box in seconds is 5mm / paper speed (e.g., 5mm / 25mm/sec = 0.2 sec).
5. Using Sample Rate (Digital ECGs): For digital ECGs, the sample rate (in Hertz, Hz) represents the number of data points acquired per second.
   • The duration of one sample is 1 / Sample Rate (in seconds).
   • The RR interval in seconds can be calculated by counting the number of samples between R-waves and multiplying by the duration of one sample.

When to Use Which Method:

The "300" method (using large boxes) is a quick estimation. The "1500" method (using small boxes) is more precise for regular rhythms. Measuring the RR interval directly in seconds is the most fundamental and can be used for both regular and irregular rhythms, though averaging over several RR intervals is recommended for irregular rhythms.

Example Calculation:

Let's assume you have an ECG strip with an RR interval of 0.80 seconds.

• Method 1 (Direct RR Interval): Heart Rate = 60 / 0.80 = 75 bpm.
• Method 3 (Small Boxes): First, calculate the number of small boxes: 0.80 seconds / 0.04 seconds/small box = 20 small boxes. Then, Heart Rate = 1500 / 20 = 75 bpm.
• Method 2 (Large Boxes): First, calculate the number of large boxes: 0.80 seconds / 0.20 seconds/large box = 4 large boxes. Then, Heart Rate = 300 / 4 = 75 bpm.

All methods, when applied correctly to the same data, yield the same result. This calculator allows you to input different parameters to see how they relate to heart rate calculation.

From RR Interval (" + rrInterval.toFixed(2) + "s):

From Large Boxes (" + largeBoxesBetweenR + "):

From Small Boxes (" + derivedSmallBoxes.toFixed(1) + "):

From Sample Rate (" + sampleRate + " Hz):