How to calculate rate in an ECG

How to calculate rate in an ECG

The heart rate can be calculated by dividing 300 by the number of large squares between each R wave (with machine trace running at the standard speed of 25 mm/sec and deflection of 1 cm/10 mV).
• 3 large squares between R waves = rate 100   
• 5 large squares = rate 60   
 Normal rate is 60–100 beats per minute (bpm).
• Rate <60 = bradycardia   
• Rate >100 = tachycardia