Heart Rate from ECG Calculator
The heart rate calculator determines BPM from an ECG by dividing 60,000 by the RR interval in milliseconds, or by counting complexes over a time period.
verified_userReviewed by the Calculopedia editorial teamLast updated 2026-08-15
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quizExample
How this calculator works, with real numbers (no JavaScript needed):
Inputs
- Calculation method
- rr
- RR interval
- 800
- Number of QRS complexes
- 5
- Time period
- 10
Results
- Heart rate
- 75
- Rhythm assessment
- Likely regular
functionsThe formula
The heart rate from an ECG is calculated in two ways, depending on whether you have a regular or irregular rhythm. The ECG is a recording of the heart's electrical activity, and the R wave — the tallest spike in the QRS complex — marks the moment the ventricles contract and pump. Measuring the spacing of those spikes is how an ECG strip reveals the heart rate.
Method 1: RR interval (regular rhythm)
Measure the time between two consecutive R waves (the tallest spikes) in milliseconds:
Heart rate = 60,000 ÷ RR interval (ms)
For an RR interval of 800 ms:
HR = 60,000 ÷ 800 = **75 BPM**
The 60,000 is simply the number of milliseconds in a minute — if one beat happens every 800 ms, then 60,000 ÷ 800 of those intervals fit into a minute. This method gives an exact rate from a single, well-measured interval, which is ideal when the rhythm is steady.
Method 2: Count complexes (irregular rhythm)
If the rhythm is irregular, count the number of QRS complexes over a known time period:
Heart rate = (number of complexes × 60) ÷ time in seconds
For 5 complexes in 10 seconds:
HR = (5 × 60) ÷ 10 = **30 BPM**
With an irregular rhythm, the RR-interval method is misleading because the spacing varies beat to beat. Averaging over a longer period with the counting method gives a far more representative figure.
Heart rate ranges
| Category | BPM |
|---|---|
| Normal (adults) | 60–100 |
| Bradycardia (slow) | Below 60 |
| Tachycardia (fast) | Above 100 |
| Athletic resting | 40–60 |
The 300-1500 rule (quick ECG reading)
On a standard ECG paper at 25 mm/s:
- 300 ÷ number of large boxes between R waves = heart rate
- Example: 4 large boxes → 300 ÷ 4 = 75 BPM
This is the same arithmetic in a different costume: each large box on ECG paper equals 0.2 seconds, so five of them make one second, and the 300 and 1500 figures just convert the box-spacing into beats per minute. It is a fast, mental-math trick that requires no ruler or calculator — handy when you are reading a strip at a glance.
Important note
This calculator provides educational estimates. Clinical ECG interpretation requires trained medical professionals. Always consult a healthcare provider for medical concerns — this content is not a substitute for professional assessment.
helpFrequently asked questions
question_markHow do I calculate heart rate from an ECG?
Use the RR interval method: divide 60,000 by the RR interval in milliseconds. For irregular rhythms, count complexes over a time period: (complexes × 60) ÷ seconds.
question_markWhat is a normal heart rate?
A normal resting heart rate for adults is 60–100 BPM. Athletes may have resting rates of 40–60 BPM. Above 100 at rest is considered tachycardia.
question_markWhat is the 300 rule on ECG?
On standard ECG paper, divide 300 by the number of large boxes between two R waves. 3 large boxes = 100 BPM, 4 = 75 BPM, 5 = 60 BPM, 6 = 50 BPM.