Identify two consecutive R waves
Measure the R–R interval in seconds
Heart rate = 60 ÷ R–R interval
If using a standard ECG at 25 mm/s, count large boxes between R waves
Heart rate = 300 ÷ number of large boxes
If using small boxes between R waves, heart rate = 1500 ÷ number of small boxes
For irregular rhythms, count QRS complexes in 6 seconds and multiply by 10
For a 10-second strip, count QRS complexes and multiply by 6
Use the method that matches the ECG paper speed and rhythm regularity