How long does one small ECG box represent?

One small ECG box represents 0.04 seconds, which is critical for interpreting an electrocardiogram (ECG). In the standard ECG graph, the horizontal axis represents time, and the small boxes that make up the larger grid are each 1 mm in height and width. Since the paper on which the ECG is printed moves at a standard speed of 25 mm per second, each small box corresponds to 1 mm, equating to 0.04 seconds (1 mm divided by 25 mm per second). Understanding this duration is essential for accurately measuring intervals such as the PR interval, QRS duration, and QT interval, which can provide valuable information about a patient’s cardiac health. This knowledge enables healthcare providers to make informed decisions regarding diagnosis and treatment based on the timing of electrical events in the heart.