β€οΈ ECG Heart Rate Calculator
From R-R boxes to beats per minute in one step.
For informational purposes only, not medical advice. Consult a healthcare professional.
Heart rate from an ECG is 300 divided by the number of large boxes between two R waves. Four large boxes means 75 bpm; two means 150. For irregular rhythms, count the QRS complexes in 6 seconds and multiply by 10. Pick your method above.
How to Use This Calculator
All heart-rate methods on ECG are the same idea: measure the time between beats, then flip it into beats per minute. The method you pick depends on whether the rhythm is regular.
For a regular rhythm, count the large boxes (or small boxes) from one R wave peak to the next. Use consecutive beats in the same lead, and average two or three intervals if they vary slightly.
For an irregular rhythm like atrial fibrillation, switch to the 6-second method: find the 3-second markers (usually notches or labels at the top of the strip), take 6 seconds (30 large boxes), count every QRS, and multiply by 10.
Read the bpm and the R-R interval. Under 60 is bradycardia, 60 to 100 is the normal resting range, over 100 is tachycardia, but context (sleep, exercise, fever, medication) decides whether any of those is a problem.
The 300 and 1500 Methods
Each large box is 0.2 seconds, so the R-R interval in seconds is 0.2 times the box count, and 60 divided by that is the rate: 60 / (0.2 x boxes) = 300 / boxes. The 1500 method is the same with small boxes (60 / 0.04 = 1500). The memorized sequence falls straight out: 300, 150, 100, 75, 60, 50 for 1 through 6 large boxes. The 6-second method skips box math entirely and works when the R-R intervals are all different, which is exactly when the box methods break down.
Worked Example
Regular rhythm, 4 large boxes between R waves: 300 / 4 = 75 bpm, R-R interval 0.80 seconds. In small boxes that is 20, and 1500 / 20 = 75, same answer. Irregular rhythm with 7 complexes in 6 seconds: 7 x 10 = 70 bpm average. A fast regular rhythm at 2 large boxes: 300 / 2 = 150 bpm, the classic rate people memorize because it sits right on the sequence. All three methods agree where they overlap; they differ only in which rhythms they handle.
What the Number Means
| Rate | Label | Common contexts |
|---|---|---|
| Under 60 | Bradycardia | Athletes, sleep, beta-blockers, hypothyroidism, conduction disease |
| 60 - 100 | Normal resting | Typical adult at rest |
| 100 - 150 | Tachycardia | Exercise, fever, anxiety, dehydration, anemia |
| Over 150 | Marked tachycardia | Often a primary arrhythmia if regular; needs evaluation |
| Over 250 | Extreme | Ventricular rhythms, pre-excited AF; emergency |
A number without a patient is just arithmetic. Sinus bradycardia at 48 in a runner is fitness; the same rate with dizziness and chest pain is not. Regular tachycardia at 150 suggests a reentrant arrhythmia like SVT or flutter; irregular tachycardia at 150 suggests atrial fibrillation. The rate tells you how fast, the regularity and the QRS width tell you what, and symptoms tell you how urgently. That is why the calculator reports the rhythm label alongside the number: rate first, interpretation second. For rates outside the ECG context, our max heart rate calculator and target heart rate zones translate bpm into exercise guidance, and our ECG boxes converter handles the interval math behind every measurement here.
Mistakes That Change the Answer
Counting from the wrong point, like peak to onset instead of peak to peak, shifts the count by a box or two. Using the 300 method on an irregular rhythm gives a different answer at every pair of beats, which is the signal to switch to the 6-second method. Atrial flutter with 2:1 conduction can look deceptively regular at 150, and mistaking flutter waves for noise leads to undercounting. And paper speed: at 50 mm/s the 300 method becomes the 600 method, a trap on fast rhythm strips. When the tracing belongs to a real patient, the machine's rate and the overreading physician's measurement outrank any hand calculation.
When the Machine Rate Is Wrong
ECG machines calculate rate automatically and print it at the top of the tracing, and most of the time they are right within a beat or two. They fail in predictable ways. Muscle tremor or a shivering patient creates artifact the machine counts as QRS complexes, inflating the rate. Tall, peaked T waves can be double-counted, turning 75 into 150. Pacemaker spikes confuse the detector in both directions. In atrial fibrillation with a slow ventricular response, the machine sometimes locks onto the f-waves instead of the QRS. The fix is always the same: put calipers (or your eyes) on the R-R interval and do the box math yourself. If your manual count disagrees with the machine by more than a few bpm, trust the manual count and mention the discrepancy to the reading physician. Machines are fast; humans are the backup.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is the 300 method on ECG?
Divide 300 by the number of large boxes between two consecutive R waves. It works because each large box is 0.2 seconds, so 60 / 0.2 = 300. It is accurate only for regular rhythms.
What is the 1500 method?
Divide 1500 by the number of small boxes between R waves. Same idea as the 300 method with finer boxes (60 / 0.04 = 1500). Useful when the R-R interval is not a whole number of large boxes.
How do you calculate heart rate in atrial fibrillation?
Use the 6-second method: count QRS complexes in 6 seconds (30 large boxes) and multiply by 10. The R-R intervals vary beat to beat in AFib, so box-count methods give a different answer each time.
What is the 300-150-100-75-60-50 rule?
The memorized heart rates for 1 through 6 large boxes between R waves: 300, 150, 100, 75, 60, 50 bpm. Rates between them are estimated by interpolation, e.g. 4.5 boxes is about 67.
What is a normal heart rate on ECG?
60 to 100 bpm at rest for adults. Well-trained athletes often rest in the 40s or 50s without it being abnormal. During exercise, rates rise toward an age-predicted maximum near 220 minus age.
How many large boxes is 60 bpm?
5 large boxes between R waves (300 / 5 = 60), which is exactly one second per beat. At 60 bpm the R-R interval is 1.0 second, a convenient calibration check.
Can you use the 300 method at 50 mm/s paper speed?
Not directly. At double speed each large box is 0.1 seconds, so the formula becomes 600 / large boxes. Always confirm the paper speed printed on the tracing before calculating.
Why does the 6-second method multiply by 10?
Because 6 seconds is one-tenth of a minute. Counting beats in 6 seconds and multiplying by 10 scales the count to a full minute. Longer strips (e.g. 30 seconds x 2) are more accurate for very irregular rhythms.
What heart rate is considered tachycardia?
Over 100 bpm at rest in adults. Sinus tachycardia from exercise, fever, or anxiety is physiologic; a sudden regular tachycardia at 150+ without exertion suggests an arrhythmia worth evaluating.
How accurate are ECG machine heart rate readings?
Usually within a few bpm for clean regular rhythms, but machines miscount with artifact, pacemaker spikes, or tall T waves mistaken for QRS complexes. Always sanity-check the machine rate against a manual R-R measurement.