Each small box on an EKG printout represents how many seconds?

Each small box on an EKG printout represents 0.04 seconds. This duration is fundamental to understanding the time intervals on an EKG strip. An EKG tracing is typically recorded at a standard speed of 25 mm/second. Since each small box is 1 mm in width, and there are 25 small boxes in one second of recording (25 mm), each small box accounts for 1/25th of a second, which converts to 0.04 seconds.

This understanding is crucial for interpreting heart rhythms as it allows healthcare professionals to measure the duration of intervals and segments, such as the PR interval, QRS duration, and QT interval, accurately by counting the small boxes on the EKG graph.