Understanding ECG Heart Rate Calculation
Electrocardiograms (ECGs) are essential tools for visualizing and analyzing the electrical activity of the heart. One of the fundamental pieces of information derived from an ECG is the heart rate, which is the number of times the heart beats per minute (BPM). There are several ways to calculate heart rate from an ECG, depending on the paper speed and the R-R interval (the time between two consecutive R waves on the ECG, which represent ventricular depolarization).
Method 1: Using the R-R Interval and ECG Paper Speed (Most Common)
The most accurate method involves measuring the R-R interval in seconds and then converting it to BPM. The standard ECG paper speed is 25 mm/second. Each small box on the ECG paper is typically 1 mm wide, representing 0.04 seconds. Each large box (made up of 5 small boxes) is 5 mm wide, representing 0.20 seconds.
The formula is: Heart Rate (BPM) = 60 / R-R Interval (seconds)
To use the grid on the ECG paper directly, you can use these shortcuts:
- If the R-R interval is exactly 1 large box: 300 BPM (60 / 0.20 seconds)
- If the R-R interval is exactly 2 large boxes: 150 BPM (60 / 0.40 seconds)
- If the R-R interval is exactly 3 large boxes: 100 BPM (60 / 0.60 seconds)
- If the R-R interval is exactly 4 large boxes: 75 BPM (60 / 0.80 seconds)
- If the R-R interval is exactly 5 large boxes: 60 BPM (60 / 1.00 seconds)
- If the R-R interval is exactly 6 large boxes: 50 BPM (60 / 1.20 seconds)
For irregular R-R intervals, you can count the number of QRS complexes (the R wave is the tallest peak in this complex) within a specific time period, usually 6 or 10 seconds, and multiply by the appropriate factor (10 for 6 seconds, 6 for 10 seconds) to estimate the average heart rate.
Method 2: Using the 3-Second Marker (for 25 mm/sec paper)
Many ECG machines have 3-second markers at the top of the tracing. These markers are typically 15 large boxes apart (15 large boxes * 0.20 sec/large box = 3 seconds). If you count the number of QRS complexes between two 3-second markers and multiply that number by 20, you get an approximation of the heart rate per minute.
The formula is: Heart Rate (BPM) ≈ Number of QRS complexes in 3 seconds * 20
About This Calculator
This calculator uses the primary method: calculating the heart rate based on the duration of the R-R interval and the standard ECG paper speed. Input the measured R-R interval in seconds to determine the heart rate in beats per minute (BPM).