ECG Heart Rate Calculator
Small Box Method (1500 Method) – Regular Rhythm
Large Box Method (300 Method) – Regular Rhythm
6-Second Method – Irregular Rhythm
Count the number of small (1mm) squares between two consecutive R waves.
Calculated Heart Rate
0 BPM
Normal Sinus Rhythm
Based on standard paper speed: 25 mm/sec
Small Box: 1mm x 1mm (0.04 sec)
Large Box: 5mm x 5mm (0.20 sec)
Vertical: 1mm = 0.1mV
Speed: 25mm/sec (Standard)
How to Calculate Heart Rate on an ECG Strip
Interpreting an Electrocardiogram (ECG/EKG) starts with determining the heart rate. Accurately calculating the beats per minute (BPM) is essential for diagnosing arrhythmias, bradycardia, and tachycardia. While modern machines provide automated readings, manual calculation remains a critical skill for verification and understanding.
Note: All calculations below assume standard ECG paper speed of 25 mm/second. If the paper speed is 50 mm/second, the results must be adjusted accordingly.
Method 1: The 1500 Method (Small Box Method)
The 1500 method is the most precise way to calculate heart rate for regular rhythms.
The Math: At a standard speed of 25 mm/s, the ECG paper travels 1,500 mm in one minute (25 mm x 60 seconds). Therefore, there are 1,500 small (1mm) boxes in one minute.
- Step 1: Identify two consecutive R waves (the peaks of the QRS complex).
- Step 2: Count the number of small squares between them.
- Step 3: Divide 1,500 by this number.
Example: If there are 20 small squares between R waves: 1500 ÷ 20 = 75 BPM.
Method 2: The 300 Method (Large Box Method)
This is a quick estimation method suitable for regular rhythms. It relies on the large grid squares (5mm x 5mm).
The Math: Since there are 5 small boxes in 1 large box, and 1500 small boxes per minute, there are 300 large boxes per minute (1500 ÷ 5 = 300).
- Step 1: Locate an R wave that lines up with a heavy vertical line (large box line).
- Step 2: Count the number of large boxes to the next R wave.
- Step 3: Divide 300 by the number of large boxes.
Quick Sequence to Memorize: 300, 150, 100, 75, 60, 50. (e.g., 1 box = 300, 2 boxes = 150, 3 boxes = 100).
Method 3: The 6-Second Method
This is the only reliable method for calculating heart rate in irregular rhythms (such as Atrial Fibrillation).
- Step 1: Obtain a 6-second strip of the ECG. ECG paper usually has hash marks at the top or bottom every 3 seconds. A 6-second strip consists of 30 large boxes.
- Step 2: Count the number of complete QRS complexes (R waves) within that 6-second period.
- Step 3: Multiply that number by 10 to get the rate for 60 seconds.
Example: If you count 8 QRS complexes in a 6-second strip: 8 x 10 = 80 BPM.
Interpreting the Results
Once you have calculated the BPM, you can categorize the heart rate:
- Normal Sinus Rhythm: 60 to 100 BPM.
- Sinus Bradycardia: Less than 60 BPM (slow heart rate).
- Sinus Tachycardia: Greater than 100 BPM (fast heart rate).