ECG Heart Rate Calculator

Enter the RR interval (distance between two R-wave peaks) measured from your ECG strip — either in millimeters or as a cycle length in milliseconds — and get the heart rate in beats per minute (bpm). Choose your paper speed (25 mm/s standard or 50 mm/s) and your preferred input method. The calculator returns the calculated heart rate along with the RR duration in seconds, helping clinicians quickly interpret ECG rhythm findings.

Disclaimer: This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions.

Input Method *

Choose how you measured the RR interval on the ECG strip.

mm

Distance between two consecutive R-wave peaks measured in millimeters.

Standard ECG paper speed is 25 mm/s. Some recordings use 50 mm/s.

msec

Time between two consecutive R-wave peaks in milliseconds.

Results

Heart Rate

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RR Duration

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Heart Rate Category

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Large ECG Boxes (RR)

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Frequently Asked Questions

What is the RR interval on an ECG?

The RR interval is the distance (in millimeters or time in milliseconds) between two consecutive R-wave peaks in the QRS complexes on an ECG strip. It represents one full cardiac cycle and is the key measurement used to calculate heart rate.

How do you calculate heart rate from an ECG?

The standard formula is: divide the RR interval in mm by the paper speed (25 mm/s) to get the RR duration in seconds, then divide 60 by that duration to get beats per minute. Alternatively, if you have the cycle length in milliseconds, divide 60,000 by the cycle length to get bpm.

What is the 300 and 1500 rule in ECG interpretation?

The '300 rule' uses large ECG boxes: divide 300 by the number of large boxes (5 mm each) between two R-waves to estimate heart rate. The '1500 rule' uses small boxes: divide 1500 by the number of small boxes (1 mm each) between R-waves. Both are quick bedside methods at standard 25 mm/s paper speed.

What paper speed is standard for ECG recordings?

The standard paper speed is 25 mm per second (mm/s). At this speed, each small square (1 mm) represents 0.04 seconds and each large square (5 mm) represents 0.2 seconds. Some countries or specific clinical situations use 50 mm/s — always verify the paper speed before calculating heart rate.

What is a normal heart rate on ECG?

A normal adult heart rate (sinus rhythm) falls between 60 and 100 beats per minute. A rate below 60 bpm is called bradycardia, and a rate above 100 bpm is called tachycardia. These thresholds guide clinical decision-making during ECG interpretation.

Can this calculator be used for irregular rhythms (arrhythmias)?

This calculator assumes a regular rhythm. If the RR intervals vary between complexes, the patient may have an arrhythmia (such as atrial fibrillation), and a single RR interval measurement may not represent the true average heart rate. In such cases, count the number of QRS complexes over a 6-second strip and multiply by 10 for a better estimate.

What is the 6-second ECG method for heart rate?

In the 6-second method, you count the number of QRS complexes within a 6-second segment of the ECG strip (marked by tick marks or counting 30 large boxes at 25 mm/s) and multiply by 10 to estimate beats per minute. This method is especially useful when the rhythm is irregular.

What is cycle length in ECG, and how does it relate to heart rate?

Cycle length is the time in milliseconds between two successive R-wave peaks. It is the inverse of heart rate: Heart Rate (bpm) = 60,000 / Cycle Length (ms). For example, a cycle length of 1000 ms equals exactly 60 bpm, while 600 ms equals 100 bpm.