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How to Calculate Heart Rate on an EKG

By Veronica Mitchell ; Updated July 27, 2017

Electrocardiography — ECG or EKG — is a non-invasive diagnostic tool. EKG measures the electrical activity of the heart using electrodes attached to the surface of the body. It can be used for a number of applications including providing a baseline reading for the activity of the heart, detection of heart rhythm disturbances or detection of a number of heart conditions. EKG readings can also be used to determine the heart rate of the patient.

Recording the EKG

Look for the operating instructions or diagrams for the EKG machine. Some machines have laminated instruction cards, or the operating manual may be available.

Prepare the patient's skin at the electrode sites by cleaning with an antiseptic wipe.

Apply the electrodes to the surface of the patient's skin using gel, lotion or pads as directed.

Connect lead wires to the electrodes as directed in the operating manual. The customary color code in the U.S. is as follows. Connect the white lead to the right arm and the black lead to the left arm. Connect the red and green leads to the left and right legs respectively, and the brown lead to the chest electrode.

Ensure the patient lies still while the EKG trace is being recorded. Movement and speech can affect the reading and result in artifacts. The patient may need to be monitored for a longer period of time if they are finding the experience stressful, as this can increase the initial heart rate.

Allow the machine to continue printing until several near-identical waves have been recorded.

Calculating Heart Rate

Identify the R waves of two consecutive heart beats. The R wave is the highest peak on the trace, and should look fairly narrow and sharp.

Count the number of large 5mm boxes between the two R waves. EKG machines are programmed such that each 5mm box represents a time of .2 seconds. The time in seconds between consecutive heart beats can therefore be calculated by multiplying the number of boxes by 5.

Calculate the heart rate by dividing 300 by the number of large 5mm boxes between the two consecutive R waves. This calculation will determine the heart rate in beats per minute.


Choose a portion of the trace where there are several waves which are close to identical, and select two consecutive R waves from the middle of this portion to perform your calculation. For a more accurate estimate of heart rate, repeat this process for several different waves and take an average.


EKG machines should only be used under appropriate medical supervision.

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