normal qrs interval
The P-R Interval. The first measurement is known as the P-R interval and is measured from the beginning of the upslope of the P wave to the beginning of the QRS wave. This measurement should be 0.12-0.20 seconds, or 3-5 small squares in duration.The second measurement is the width of the QRS which should be less than 3 small squares, or less than 0.12 seconds in duration. Image: Normal Intervals. 1  P-R interval = 0.12 - 0.20 sec (3 - 5 small squares).2  QRS width = 0.08 - 0.12 sec (2 - 3 small squares). 3  Q-T interval 0.35 - 0.43 sec. P-R interval = 0.12 - 0.20 sec (3 - 5 small squares). 2  QRS width = 0.08 - 0.12 sec (2 - 3 small squares). 3  Q-T interval 0.35 - 0.43 sec. * 4  The PR interval should really be referred to as the PQ interval; however it is commonly referred as the PR interval.