ECG Heart Rate Calculator
Understanding ECG and Heart Rate Calculation
An electrocardiogram (ECG or EKG) is a vital diagnostic tool that records the electrical activity of the heart over time. This electrical activity creates waveforms that can be interpreted to assess heart rhythm, rate, and overall cardiac health.
One common method for calculating heart rate from an ECG relies on the relationship between the R-R interval (the time between two consecutive R waves on the QRS complex) and the speed at which the ECG paper is moving. The R-R interval represents one cardiac cycle.
The Formula:
Heart Rate (beats per minute) = (60 seconds/minute) / (R-R Interval in seconds)
Since ECG paper often has standardized markings, we can use the number of small boxes (each typically representing 0.04 seconds) or large boxes (each typically representing 0.20 seconds) to determine the R-R interval. The standard paper speed is usually 25 mm/sec, meaning each small box is 1 mm wide and represents 0.04 seconds.
To simplify calculations using small boxes:
- R-R Interval in seconds = Number of small boxes × 0.04 seconds/small box
- Heart Rate (bpm) = 60 / (Number of small boxes × 0.04)
Alternatively, if you know the paper speed, you can use:
- Heart Rate (bpm) = (Number of large boxes between R-R × 5) – This is a shortcut for 25 mm/sec paper, as 300 large boxes per minute.
- Heart Rate (bpm) = 1500 / Number of small boxes between R-R – Another shortcut for 25 mm/sec paper, as 1500 small boxes per minute.
This calculator uses the "Number of small boxes" and "Calibration Paper Speed" to provide an accurate heart rate calculation.
Example:
If the R-R interval on an ECG strip is measured to be 20 small boxes, and the paper speed is the standard 25 mm/sec (meaning each small box is 0.04 seconds):
- R-R interval in seconds = 20 small boxes × 0.04 sec/box = 0.8 seconds
- Heart Rate = 60 / 0.8 = 75 beats per minute (bpm)
Using the shortcut for 25 mm/sec paper:
- Heart Rate = 1500 / 20 small boxes = 75 bpm