Heart Rate Calculator (R-R Interval)
Convert ECG intervals to Beats Per Minute (BPM)
Milliseconds (ms)
Seconds (s)
Small Squares (0.04s / 1mm)
Large Squares (0.20s / 5mm)
Enter the time between two consecutive R-waves.
Calculated Heart Rate
0 BPM
How to Calculate Heart Rate from R-R Interval
The R-R interval is the time elapsed between two successive R-waves of the QRS signal on an electrocardiogram (ECG). Calculating heart rate from this interval is the most accurate method for determining ventricular rate, provided the rhythm is regular.
The Core Formula:
Heart Rate (BPM) = 60 / R-R Interval (in seconds)
Heart Rate (BPM) = 60 / R-R Interval (in seconds)
Understanding the Calculation Methods
Depending on how you measure the R-R interval, the formula changes slightly:
1. Using Time (Milliseconds or Seconds)
Digital ECG machines often provide the R-R interval in milliseconds. Since there are 60,000 milliseconds in a minute, the formula is:
- Formula: 60,000 ÷ R-R Interval (ms) = BPM
- Example: If the interval is 800ms, the Heart Rate is 60,000 ÷ 800 = 75 BPM.
2. The 1500 Method (Small Squares)
On standard ECG paper (running at 25 mm/sec), one small square represents 0.04 seconds (40ms). This is often called the "1500 method" because 60 seconds ÷ 0.04 seconds = 1500.
- Formula: 1500 ÷ Number of Small Squares = BPM
- Example: If there are 20 small squares between R peaks, the HR is 1500 ÷ 20 = 75 BPM.
3. The 300 Method (Large Squares)
One large square on ECG paper consists of 5 small squares and represents 0.20 seconds (200ms). This is a quick estimation method often used in clinical settings.
- Formula: 300 ÷ Number of Large Squares = BPM
- Example: If there are 4 large squares between R peaks, the HR is 300 ÷ 4 = 75 BPM.
Interpreting the Results
For a resting adult, heart rates are generally classified as follows:
- Bradycardia: Less than 60 BPM. This is common in athletes or during sleep but can indicate pathology in others.
- Normal Sinus Rhythm: 60 to 100 BPM.
- Tachycardia: Greater than 100 BPM. This can be caused by exercise, stress, or cardiac arrhythmias.
Note: This calculator assumes a regular rhythm. In the presence of arrhythmias (like Atrial Fibrillation), the R-R interval varies beat to beat, and an average over usually 6 or 10 seconds is required for accuracy.