74 Large Boxes on EKG = 14.8 Seconds
On a standard ECG recorded at 25 mm/s paper speed, 74 large boxes represents 14.8 seconds.
Calculation
Each large box on standard ECG paper represents:
- 5 mm horizontally
- At the standard recording speed of 25 mm/s, each large box = 0.2 seconds (or 200 milliseconds)
Therefore:
- 74 large boxes × 0.2 seconds/box = 14.8 seconds
Standard ECG Paper Speed
The American Heart Association guidelines establish that standard ECG recording uses 25 mm/s paper speed 1. At this speed:
- Each small box (1 mm) = 0.04 seconds (40 ms)
- Each large box (5 mm) = 0.2 seconds (200 ms)
- 5 large boxes = 1 second
- 37 large boxes = 7.4 seconds (approximately the length of one standard column on a 12-lead ECG)
Clinical Context
Standard 12-lead ECG printouts typically display four 2.5-second columns (each containing 12.5 large boxes), creating a continuous 10-second recording 1. Your measurement of 74 large boxes would span nearly three full columns of a standard ECG printout, representing approximately 15 seconds of cardiac electrical activity.
Common Pitfall
Always verify the paper speed on the ECG printout—while 25 mm/s is standard, some recordings use 50 mm/s (where each large box would represent only 0.1 seconds instead of 0.2 seconds). The paper speed is typically printed at the bottom of the ECG tracing.