All full-width elements, like The Grid, Grid Repeater, and Text in containers, are set to 100% width.

Width Property

We can see the actual value in percentage, for example, 100%, in the Property Panel value.

full-width-grid.png

Enter Value In Percentage

You can set the Width value in percentage.

width-height-in-percent.png

NOTE: Unlike Width, you can set the Height value ONLY to 100%.