ECG Rate Calculator
Calculate heart rate from an electrocardiogram strip using standard clinical methods.
Small Square Method (Most Accurate)
Large Square Method (Quick Estimate)
6-Second Strip Method (Irregular Rhythms)
Best for regular rhythms. Count small boxes between R-R intervals.
25 mm/sec (Standard)
50 mm/sec
Heart Rate
0 BPM
How to Calculate Rate on an ECG
Calculating the heart rate from an electrocardiogram (ECG or EKG) is a fundamental skill for medical professionals, paramedics, and students. The method you choose depends largely on whether the heart rhythm is regular or irregular, and the level of precision required.
Understanding the ECG Grid
Before calculating the rate, it is crucial to understand the standard ECG paper calibration:
- Standard Paper Speed: 25 mm/second.
- Small Square: 1 mm x 1 mm, representing 0.04 seconds.
- Large Square: 5 mm x 5 mm (5 small squares), representing 0.20 seconds.
Note: If the paper speed is set to 50 mm/sec, the time values double (1 large square = 0.10 seconds), requiring adjustments to standard formulas.
Method 1: The 1500 Method (Small Square Method)
This is the most accurate method for calculating heart rate for regular rhythms.
The Formula
Heart Rate = 1500 / Number of Small Squares between R-R interval
How to use it:
- Identify two consecutive R waves (the peaks of the QRS complex).
- Count the number of small squares between them.
- Divide 1500 by this number.
Example: If there are 20 small squares between two R waves: 1500 ÷ 20 = 75 BPM.
Method 2: The 300 Method (Large Square Method)
This method is faster but less precise, suitable for quick estimation of regular rhythms.
The Formula
Heart Rate = 300 / Number of Large Squares between R-R interval
How to use it:
- Find an R wave that lands on a heavy black line (start of a large square).
- Count the number of large squares to the next R wave.
- Divide 300 by this count.
Example: If there are 4 large squares between R waves: 300 ÷ 4 = 75 BPM.
Alternatively, you can memorize the sequence for each subsequent large line: 300, 150, 100, 75, 60, 50.
Method 3: The 6-Second Method
This is the only reliable method for calculating heart rate in irregular rhythms (e.g., Atrial Fibrillation).
The Formula
Heart Rate = Number of R waves in a 6-second strip x 10
How to use it:
- Obtain a 6-second strip of the ECG (usually marked by 3-second hash marks at the top or bottom of the paper, covering 30 large squares).
- Count the number of QRS complexes (R waves) within this 6-second period.
- Multiply the count by 10.
Example: If you count 8 QRS complexes in the 6-second strip: 8 x 10 = 80 BPM.
Normal Heart Rate Ranges
| Condition | Rate Range (BPM) |
|---|---|
| Bradycardia | < 60 BPM |
| Normal Sinus Rhythm | 60 – 100 BPM |
| Tachycardia | > 100 BPM |