ECG Grid to Seconds Calculator

How to Use ECG Grid to Seconds Calculator

Use ECG Grid to Seconds Calculator when reading intervals on standard ECG paper. Count the number of small boxes, large boxes, or both, then enter those counts to convert the grid distance into seconds and milliseconds.

If your ECG was printed or displayed at a different paper speed, do not use this result without adjustment. At 50 mm/s, for example, each small box represents half the time used here.

Formula & Theory - ECG Grid to Seconds Calculator

The core calculation is:

At 25 mm/s:
1 small box = 0.04 seconds
1 large box = 5 small boxes = 0.20 seconds
Total seconds = small boxes × 0.04 + large boxes × 0.20

ECG paper speed defines the time scale. At 25 mm/s, one millimeter travels under the stylus in 0.04 seconds. A large box contains five small boxes, so it represents 0.20 seconds.

This conversion is the basis for measuring PR interval, QRS duration, QT interval, pauses, and rhythm strip timing. Accuracy depends on paper speed, grid visibility, and where the interval boundaries are chosen.

Use Cases for ECG Grid to Seconds Calculator

Use it while studying ECG interpretation, checking manual interval measurements, or teaching how grid boxes map to real time.

It is also useful when converting a rhythm-strip pause into seconds before comparing it with clinical thresholds or monitor readouts.