ECG Heart Rate Calculator
1500 Method (Small Squares – Most Precise)
300 Method (Large Squares – Quick Est.)
6-Second Strip Method (Irregular Rhythm)
Assumes standard paper speed of 25mm/sec
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Beats Per Minute (BPM)
How to Calculate Heart Rate on an ECG
Interpreting an electrocardiogram (ECG or EKG) is a fundamental skill in cardiology and emergency medicine. While modern machines often provide an automated heart rate, calculating it manually is crucial for verification, especially when artifacts or arrhythmias are present. The method you choose depends largely on the regularity of the heart rhythm.
Understanding the ECG Grid
To calculate heart rate accurately, you must understand the standard ECG paper calibration:
- Standard Speed: 25 mm/second.
- Small Square: 1 mm x 1 mm (represents 0.04 seconds).
- Large Square: 5 mm x 5 mm (represents 0.20 seconds).
- One Large Square: Contains 5 small squares horizontally.
Method 1: The 1500 Method (Precise)
The 1500 method is the most accurate way to determine heart rate for regular rhythms. It uses the small squares on the ECG paper.
Formula: 1500 ÷ Number of Small Squares between two consecutive R waves
Example: If there are 20 small squares between two R waves, the heart rate is 1500 / 20 = 75 BPM.
Method 2: The 300 Method (Quick Estimation)
The 300 method (also known as the Sequence Method) is great for a quick bedside estimation for regular rhythms. It relies on the large grid squares (5mm).
Formula: 300 ÷ Number of Large Squares between two consecutive R waves
| Large Squares between R-R | Calculated Heart Rate (BPM) |
|---|---|
| 1 | 300 BPM |
| 2 | 150 BPM |
| 3 | 100 BPM |
| 4 | 75 BPM |
| 5 | 60 BPM |
| 6 | 50 BPM |
Method 3: The 6-Second Method (Irregular Rhythms)
When the heart rhythm is irregular (such as in Atrial Fibrillation), the R-R intervals vary, making the 300 and 1500 methods inaccurate. In these cases, the 6-second method provides an average rate.
Steps:
- Identify a 6-second strip on the ECG paper (30 large squares).
- Count the number of QRS complexes (R waves) within that 6-second period.
- Multiply the count by 10.
Example: If you count 8 QRS complexes in a 6-second strip, the rate is 8 x 10 = 80 BPM.
Clinical Interpretation of Heart Rate
- Normal Sinus Rhythm: 60 – 100 BPM.
- Bradycardia: Less than 60 BPM.
- Tachycardia: Greater than 100 BPM.