Calculating Heart Rate on an EKG

As technology continues to advance, its helped us create shortcuts for our everyday lives. Gone are the days of searching through phone books for a friend’s house line, taking notes with a pad and pen, and even calculating heart rate.

Normally, the software on a cardiac stress test unit calculates heart rate. But what happens if the unit broke? Being able to calculate heart rate on a rhythm strip is an excellent skill to have as a healthcare provider in the event of a power outage or system malfunction. In today’s blog, we’re going to go over how to do this.

The How

An EKG strip is a grid where time is measured along the horizontal axis of the paper. Small squares are 1mm in length representing .04 seconds while large squares are 5mm in length representing .20 seconds. 15 big squares equal 3 seconds of time while 30 big squares equal 6 seconds.

For regular heart rhythms, the heart rate is 300 divided by the number of large squares between the QRS complexes. For example, if there are5 large squares between regular QRS complexes, the heart rate is 60 (300/5=60).

For irregular rhythms, count the number of R waves in a 6 second strip and multiply by 10. For example, if there are 8 R waves in a 6 second strip, the heart rate is 80 (8×10=80).


Today, we seldom need to worry about calculating EKG from scratch. However, its a handy skill to add to a clinicians back pocket if the need ever arose. Not only is it useful, its simple as well!