You would typically use inches or millimeters to measure the width of a sheet of paper.

Here's why:

* Inches: This is the standard unit of measurement in the US and some other countries.

* Millimeters: This is the standard unit of measurement in many other countries, including the metric system.

You might see paper sizes like:

* 8.5 inches x 11 inches (Letter size)

* 210 millimeters x 297 millimeters (A4 size)

Let me know if you have any other questions!