RR Interval to Heart Rate Calculator
What is the RR Interval?
In electrocardiography (ECG), the RR interval is the time elapsed between two successive R waves of the QRS signal on the electrocardiogram. It represents the duration of one complete cardiac cycle. Measuring this interval is the most accurate way to determine the instantaneous heart rate and assess heart rate variability (HRV).
The Heart Rate Formula
To calculate heart rate from the RR interval, we use a simple reciprocal mathematical relationship. Since there are 60 seconds in a minute (or 60,000 milliseconds), the formulas are:
- If using milliseconds (ms): BPM = 60,000 / RR Interval
- If using seconds (s): BPM = 60 / RR Interval
Clinical Significance of RR Intervals
Analyzing RR intervals is crucial for identifying cardiac arrhythmias. A consistent RR interval suggests a regular rhythm, while significant variations can indicate conditions like Atrial Fibrillation or Premature Ventricular Contractions (PVCs).
| RR Interval (ms) | BPM (Approx) | Classification (Adults) |
|---|---|---|
| > 1000 ms | < 60 BPM | Bradycardia (Slow) |
| 600 – 1000 ms | 60 – 100 BPM | Normal Resting Rate |
| < 600 ms | > 100 BPM | Tachycardia (Fast) |
How to Measure RR Interval on ECG Paper
On standard ECG paper moving at 25mm/sec, each "large box" (5mm) represents 0.2 seconds (200ms) and each "small box" (1mm) represents 0.04 seconds (40ms). To find the RR interval, count the number of small boxes between two R peaks and multiply by 40.