Regular rhythms can be quickly determined by counting the number of large graph boxes between two consecutive R waves. That number is divided into 300 to calculate bpm. This method does not give exact rates, but is close enough for rapid rate calculation. The rates for the first one to six large boxes can be easily memorized.

Remember: 60 sec/minute divided by 0.20 sec/large box = 300 large boxes/min. This method usually gives an approximate heart rate but is not as accurate as method 2, explained next.