Identify the onset of the QRS complex at the first deflection from the baseline
Identify the end of the QRS complex at the point where the waveform returns to the baseline
Measure the duration from onset to end using the ECG paper time scale
Count small boxes between onset and end
Multiply the number of small boxes by 0.04 seconds
Or count large boxes and multiply by 0.20 seconds
Use the widest QRS complex if measuring across multiple leads
Record the QRS duration in seconds or milliseconds
Compare the result with normal QRS duration values
Note any widening, notching, or fragmentation if present