We can easily calculate heart rate from the ECG strip using one of the following methods: - If the rhythm is regular, we calculate heart rate by taking the value of 300 and dividing it by the number of squares between the QPS complexes. For instance, suppose there are 5 large squares between the complexes, then the heart rate is 300 / 5 = 60 - The second method for calculating the heart rate is if the rhythm is irregular. You need to multiply how many R waves you have in a six-second strip by 10. For instance, we counted 8 R waves; the heart rate would be 8 x 10 = 80