ECG Small-Box Converter

How to calculate ECG box duration?

ECG paper moves at a constant speed, meaning horizontal distance represents time. Each 1mm small box translates to a specific duration.

Formula: Time (ms) = (Boxes × 1000) / Speed

Using the ECG converter: an example

For a standard measurement of 4 small boxes at a paper speed of 25 mm/s:

Step-by-step calculation:

• Divide 1 second by the speed: 1 / 25 = 0.04 seconds per box.
• Multiply by box count: 4 × 0.04 = 0.16 seconds.
• Convert to milliseconds: 0.16 × 1000 = 160 ms.

Frequently Asked Questions

What is the duration of a large box?

A large box consists of 5 small boxes. At standard 25 mm/s speed, one large box equals 0.20 seconds or 200 ms.

When is 50 mm/s paper speed used?

Higher paper speeds are often used to better visualize complex arrhythmias or pediatric ECGs by stretching out the waveforms.

Is this calculation the same for vertical boxes?

No, vertical boxes measure voltage (amplitude) in millivolts (mV), where 10 small boxes usually equal 1 mV.