How this calculator works
The reciprocal of the RR interval gives cycles per second; multiplying by 60 gives beats per minute. Box mode first converts horizontal grid distance to seconds. A single RR measurement describes an instantaneous rate and assumes comparable successive beats. Average several intervals for variable rhythms; this tool does not identify arrhythmias. The result is an estimate for information only and is not medical advice.
Formula
HR = 60 / RR(s). With boxes, RR = boxes × width(mm) / speed(mm/s).
Worked example
RR 0.8 s gives 75 beats/min. Three large boxes at 25 mm/s give RR 0.6 s and 100 beats/min.
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Frequently asked questions
Which peaks do I measure?
Measure between matching R peaks in successive cardiac cycles.
What if the rhythm is irregular?
A single interval may be unrepresentative. Clinical interpretation needs a longer recording.
Why does paper speed matter?
The same number of boxes represents half the time at 50 versus 25 mm/s.