ECG Heart Rate Calculator
Calculate BPM using standard paper speed (25mm/sec) methods
Easy Ways to Calculate Heart Rate on an ECG Strip
Interpreting an ECG (Electrocardiogram) usually starts with determining the heart rate. While modern machines provide automated numbers, knowing how to manually calculate the rate is a critical skill for healthcare professionals, students, and technicians, especially when verifying machine accuracy or dealing with artifacts.
1. The 300 Method (Large Box Method)
This is the quickest and easiest way to calculate heart rate on an ECG strip, provided the heart rhythm is regular. Standard ECG paper moves at a speed of 25mm/second.
The Math: There are 300 large boxes (5mm each) in one minute. Therefore, you calculate the rate by dividing 300 by the number of large squares between two consecutive R waves (the peaks of the QRS complex).
- Formula: 300 ÷ Number of Large Squares
- Example: If there are 4 large squares between R waves, the heart rate is 300 ÷ 4 = 75 BPM.
2. The 1500 Method (Small Box Method)
This is the most precise method for regular rhythms. It uses the small 1mm boxes found inside the large boxes.
The Math: There are 1,500 small boxes (1mm each) in one minute of ECG recording. You count the specific number of small squares between two consecutive R waves.
- Formula: 1500 ÷ Number of Small Squares
- Example: If there are 20 small squares between R waves, the heart rate is 1500 ÷ 20 = 75 BPM.
3. The 6-Second Method
This is the only reliable method for calculating heart rate when the rhythm is irregular (such as in Atrial Fibrillation).
The Math: Standard ECG paper has time markers every 3 seconds (often marked by a hash mark at the top or bottom). You take a 6-second strip (usually 30 large boxes) and count the number of QRS complexes (R waves) within that period.
- Formula: (Number of R waves in 6 seconds) × 10
- Example: If you count 8 R waves in a 6-second strip, the heart rate is approximately 8 × 10 = 80 BPM.
Interpreting the Results
Once you have the beats per minute (BPM), you can classify the rate:
- Bradycardia: Less than 60 BPM.
- Normal Sinus Rhythm: 60 to 100 BPM.
- Tachycardia: Greater than 100 BPM.