ECG Heart Rate
Calculate heart rate from an ECG strip using the RR interval formula, 300/1500 rule, or 6-second method. Free online ECG heart rate calculator for medical professionals.
About This Calculator
The ECG Heart Rate Calculator is a practical tool for healthcare professionals, medical students, and clinicians to quickly and accurately determine heart rate from an electrocardiogram (ECG) strip. It supports three calculation methods — the RR interval formula, the 300/1500 rule using ECG boxes, and the 6-second method for irregular rhythms — making it versatile for both regular and irregular cardiac rhythms.
The primary formula used is Heart Rate (BPM) = 60,000 ÷ RR Interval (ms). The RR interval is the time between two consecutive R wave peaks on the ECG. When using the boxes method, each small box (1 mm) represents 0.04 seconds at 25 mm/s, and each large box (5 mm) represents 0.20 seconds. The 300 rule (300 ÷ number of large boxes) and 1500 rule (1500 ÷ number of small boxes) are quick clinical shortcuts derived from this formula. For irregular rhythms, the 6-second method counts QRS complexes over 30 large boxes (6 seconds) and multiplies by 10 to estimate average heart rate.
A normal resting heart rate for adults ranges from 60 to 100 BPM. Rates below 60 BPM indicate bradycardia, which may be normal in athletes, while rates above 100 BPM indicate tachycardia. Children have higher normal ranges: newborns 100–160 BPM, infants 80–140 BPM, and older children 60–120 BPM. Accurate heart rate calculation is essential for diagnosing arrhythmias, assessing hemodynamic stability, and monitoring cardiac health.
Frequently Asked Questions
How do I calculate heart rate from an ECG?
Measure the RR interval (distance between two consecutive R waves) in milliseconds and divide 60,000 by that value. Alternatively, count the number of large boxes between R waves and divide 300 by that number (300 rule), or count small boxes and divide 1500 by that number (1500 rule). For irregular rhythms, use the 6-second method by counting QRS complexes in a 6-second strip and multiplying by 10.
What is a normal heart rate on ECG?
A normal resting heart rate for adults is between 60 and 100 beats per minute (BPM) on ECG. A rate below 60 BPM is called bradycardia, and above 100 BPM is called tachycardia. In children, normal heart rate ranges are higher and vary by age.
What is the 300 rule for ECG heart rate?
The 300 rule is a quick method to estimate heart rate from an ECG. Count the number of large boxes (5 mm each) between two consecutive R waves, then divide 300 by that number. For example, 4 large boxes between R waves gives 300 ÷ 4 = 75 BPM. This works at standard paper speed of 25 mm/s.
What is the 1500 rule for ECG heart rate?
The 1500 rule provides a more precise estimate than the 300 rule. Count the number of small boxes (1 mm each) between two consecutive R waves, then divide 1500 by that number. Since each small box represents 0.04 seconds at 25 mm/s, this method gives a more accurate heart rate calculation.
How do I use the 6-second method for irregular heart rhythms?
For irregular rhythms like atrial fibrillation, use the 6-second method. Print a 6-second ECG strip (30 large boxes at 25 mm/s), count the number of QRS complexes in that strip, and multiply by 10. This gives an average heart rate in BPM that accounts for the irregularity.
What is the standard ECG paper speed?
The standard ECG paper speed is 25 mm/s, where each small box (1 mm) equals 0.04 seconds and each large box (5 mm) equals 0.20 seconds. Some ECG machines also offer 50 mm/s for detailed analysis, where small boxes equal 0.02 seconds and large boxes equal 0.10 seconds.
Can this calculator be used for pediatric ECG interpretation?
Yes, the calculator works for all ages. However, normal heart rate ranges differ for children: newborns 100-160 BPM, infants 80-140 BPM, and older children 60-120 BPM. Always consult pediatric-specific normal ranges when interpreting ECGs in children.
What if the RR intervals are irregular on the ECG?
If RR intervals vary significantly between beats, the patient may have an arrhythmia such as atrial fibrillation. In this case, the 300/1500 rule methods may give inaccurate results. Use the 6-second method instead, which averages the heart rate over a longer strip for a more representative measurement.