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How to Calculate Heart Rate & EKG

The electrocardiogram (EKG) is a tool that your physician can use to gauge how your heart is working without actually seeing your heart 1. According to Net Doctor, the electrocardiogram measures the electrical activity of the heart while it is beating 1. Changes in the waveforms created by this activity aid physicians and other health care professionals in diagnosing certain conditions you may have or changes made by certain medications during your treatment. You should see your physician for medical attention immediately if you think you are having problems, such as your heart beating too fast or too slow.

Attach the individual EKG wires to electrodes, and adhere them to their respective positions on the person’s body. The white lead, or the one marked RA, should be adhered to the right arm. The black lead, or the one marked LA, should be adhered to the left arm. The red lead, or the one marked LL, should be adhered to the left leg.

What Are the Four Parts of the EKG Machine?

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Print a six-second strip of EKG paper (at least 30 boxes). Ensure that there is a waveform on the printout that is clear and free of artifact or lines that move all over the printout, called a wandering baseline. According to McGill, the paper uses a graph to identify time (horizontal boxes) versus the signal strength, or amplitude (vertical boxes). If the printout is persistently poor, ensure the patient is lying still and that the electrodes are properly adhered.

Identify the sharp upward spike of the QRS complex called the R-wave. According to Cardiovascular Physiology Concepts, the R-wave specifically represents the contraction of the lower chambers of the heart, called ventricles 2. R-waves may be spaced evenly or unevenly on the printout, depending on the person.

Use the heart rate calipers to determine if the heart rate is regular or irregular by placing the needle tips on two contiguous R-waves. Move the calipers so that the first needle is on the second R-wave, and the second needle is on the next contiguous R-wave. If the R-waves match along the entire printout, the rate is considered regular.

How to Count the Boxes on the EKG Paper to Determine Rate

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Calculate the heart rate using the Rule 1500. According to Basic Dysrhythmias: Interpretation and Management, each horizontal box equals 0.04 seconds 3. Therefore, count the number of small squares between two contiguous R-waves and divide that number into 1500. For example, if 17 small squares are between two contiguous R-waves, the heart rate is 88 (1500/17 = 88).

If the heart rate is irregular, calculate the average number of small boxes between contiguous R-waves in the entire six-second printout. For example, if 17 small boxes are between the first two R-waves, 13 between the second and third, 20 between the third and fourth, 18 between the fourth and fifth and 12 between the fifth and sixth, the heart rate equals 94 (1500/(17+13+20+18+12/5)).


The red lead, or the one marked LL, can be adhered to the left side of the abdomen if the printout is persistently poor.

Ensure that the centers of the electrodes are gel-like in consistency for the best waveform.

The Rule 1500 will yield an average heart rate for irregular rhythms.


The EKG is a static test, and only measures a small window of time in the overall workload of your heart.

This technique should not be used to diagnose or treat any condition. Consult your physician or medical professional for a specific diagnosis and treatment.