About the ECG Heart Rate Calculator
This calculator converts what you see on an electrocardiogram (ECG/EKG) into a heart rate in beats per minute. Standard ECG paper runs at 25 mm per second, so each small 1 mm box is 0.04 seconds and each large 5 mm box is 0.20 seconds. That gives the classic shortcuts: 300 divided by the number of large boxes between two R waves, 1500 divided by the number of small boxes, or — for irregular rhythms — the number of QRS complexes in a 6-second strip multiplied by 10.
Choose the method that matches your strip. The large-box (300) method is the fastest bedside estimate for regular rhythms, the small-box (1500) method is the most precise for regular rhythms, and the 6-second method is the one to use for irregular rhythms such as atrial fibrillation, because it averages the rate over several beats. You can also enter an R-R interval in milliseconds if your machine measures it, and switch the paper speed to 50 mm/s, which is common in some European countries and paediatric settings.
It is a teaching and quick-check tool for students, nurses, paramedics and clinicians learning ECG interpretation. The rate category uses the conventional adult resting range of 60–100 bpm; children have higher normal rates, and the rhythm itself still needs to be interpreted on the full ECG.
With the default inputs, the heart rate is 75 bpm. Change any value above to recalculate instantly.
How to use the ecg heart rate calculator
- 1Choose the method: box counting for regular rhythms, 6-second for irregular ones.
- 2Check the paper speed printed on the ECG (usually 25 mm/s).
- 3Count the boxes between two consecutive R waves, or the QRS complexes in the strip.
- 4Enter the count and read the heart rate and rate category.
Formula and method
At 25 mm/s there are 300 large boxes (0.2 s each) and 1,500 small boxes (0.04 s each) in one minute, so dividing 300 or 1,500 by the number of boxes in one R-R interval gives beats per minute. At 50 mm/s the paper moves twice as fast, so the constants double to 600 and 3,000.
The 6-second method counts QRS complexes across a 6-second strip and multiplies by 10 (or by 6 for a 10-second strip), averaging the rate across an irregular rhythm. The R-R interval is the reciprocal of rate: 60,000 ms ÷ R-R in ms.
- HR
- Heart rate (beats per minute)
- R-R
- Time between two consecutive R waves
Worked examples
300 method: 4 large boxes
At 25 mm/s, 300 ÷ 4 large boxes = 75 bpm. Each large box is 0.2 s, so the R-R interval is 0.8 s or 800 ms.
1500 method: 12 small boxes
1500 ÷ 12 small boxes = 125 bpm, a sinus or other tachycardia. The R-R interval is 12 × 40 ms = 480 ms.
6-second method in atrial fibrillation
Five irregular QRS complexes in a 6-second strip × 10 = 50 bpm, a slow average ventricular rate.
Paper at 50 mm/s
At 50 mm/s each large box is only 0.1 s, so the constant doubles: 600 ÷ 6 = 100 bpm.
Frequently asked questions
How do you calculate heart rate from an ECG?+
For a regular rhythm at 25 mm/s, divide 300 by the number of large boxes between two R waves, or 1500 by the number of small boxes. For an irregular rhythm, count the QRS complexes in a 6-second strip and multiply by 10.
Which ECG heart rate method is most accurate?+
For regular rhythms the 1500 (small box) method is the most precise because it uses the smallest unit of time. For irregular rhythms such as atrial fibrillation, the 6-second (or 10-second) count is more representative because it averages several beats.
What is the sequence 300, 150, 100, 75, 60, 50?+
It is the rate when the next R wave falls on the 1st, 2nd, 3rd, 4th, 5th or 6th thick line after an R wave on a heavy line. It is a fast way to estimate rate from a standard 25 mm/s strip.
What is a normal heart rate on an ECG?+
For adults at rest the conventional range is 60–100 bpm; below 60 is bradycardia and above 100 is tachycardia. Fit adults may normally have rates in the 40s–50s, and children have higher normal ranges by age.
For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.