Certified EKG Technician (CET) Practice Exam 2026 – Comprehensive Test Prep

The method of dividing 300 by the number of large boxes between two R waves is a well-established technique for calculating heart rate from an EKG tracing. This approach is based on the standard EKG paper speed, which is 25 mm per second. Since each large box on the EKG paper represents 0.2 seconds (5 small boxes per large box), dividing 300 by the number of large boxes gives a direct calculation of how many beats per minute (BPM) correspond to the heart rhythm observed.

For example, if there are 3 large boxes between two R waves, you would perform the calculation: 300 ÷ 3 = 100 BPM. This method is fast and reliable, especially for regular rhythms, making it a preferred technique among EKG technicians.

Counting the number of R waves in 10 seconds and multiplying by 6 can yield an accurate heart rate but requires an overall analysis over a set timeframe rather than directly assessing the spaces on the tracing. Counting the number of small boxes between R waves is useful for determining the heart rate using a different formula, but it is less direct than the method of dividing 300 by large boxes. Multiplying the total number of QRS complexes by 10 does not provide