Which formula uses the number of large boxes between R waves to calculate heart rate?

Which formula uses the number of large boxes between R waves to calculate heart rate?

• A. Heart Rate = 1500 / # of small boxes between R waves
• B. Heart Rate = 60 / # of large boxes between R waves
• C. Heart Rate = 300 / # of large boxes between R waves
• D. Heart Rate = 1500 / # of large boxes between R waves

Answer: (C)

On ECG paper at the standard speed, each large box represents 0.2 seconds. The R-R interval is how long one cardiac cycle takes, so if there are N large boxes between R waves, the interval is 0.2 × N seconds. Heart rate is beats per minute, which is 60 seconds per minute divided by that interval: 60 / (0.2 × N) = 300 / N. So the formula using the number of large boxes between R waves is Heart Rate = 300 divided by the number of large boxes between R waves. For example, with 5 large boxes between R waves, HR = 300/5 = 60 bpm. The other approaches either use small boxes (HR = 1500 / small boxes) or mix incorrect coefficients, which doesn’t reflect the 0.2-second value of a large box.

On ECG paper at the standard speed, each large box represents 0.2 seconds. The R-R interval is how long one cardiac cycle takes, so if there are N large boxes between R waves, the interval is 0.2 × N seconds. Heart rate is beats per minute, which is 60 seconds per minute divided by that interval: 60 / (0.2 × N) = 300 / N. So the formula using the number of large boxes between R waves is Heart Rate = 300 divided by the number of large boxes between R waves. For example, with 5 large boxes between R waves, HR = 300/5 = 60 bpm. The other approaches either use small boxes (HR = 1500 / small boxes) or mix incorrect coefficients, which doesn’t reflect the 0.2-second value of a large box.