EKG Strip Measurement: Time Intervals
On a standard EKG strip, 10 small squares equal 2 seconds.
Understanding EKG Paper Standardization
Standard EKG paper has a grid pattern with both small and large squares:
- Each small square = 0.04 seconds (1 mm width)
- Each large square (5 small squares) = 0.20 seconds (5 mm width)
- 10 small squares = 0.40 seconds
- 25 small squares = 1 second
- 50 small squares = 2 seconds
Practical Application
When interpreting an EKG strip:
- Count the number of small squares to determine time intervals
- For a 2-second measurement, count 50 small squares horizontally
- Alternatively, count 10 large squares (each large square contains 5 small squares)
Clinical Significance
Understanding the time scale on EKG paper is critical for:
- Accurate heart rate calculation
- Proper interval measurements (PR, QRS, QT intervals)
- Rhythm interpretation
- Recognition of conduction abnormalities
Common Pitfalls to Avoid
- Confusing small squares with large squares when counting
- Miscounting when the paper speed is different from the standard 25 mm/second
- Failing to recognize when non-standard paper speeds are used (some systems may use 50 mm/second, which would double the number of squares for a given time interval)
The standardization of EKG paper at 25 mm/second means that 50 small squares or 10 large squares consistently represent 2 seconds, allowing for uniform interpretation across different recording systems 1.