Scale illustrator icon to take up the maximum available space

I am creating icons, and all of them should take up as much space as possible in an 256x256 image.

It happens quite often that I do not perfectly meet this requirement when I design the icon.

For example, my icon is only 250 pixels high instead of 256 pixels. Then I need to manually scale the object up in order to use as much space as possible so that there are no unused pixels.

I would like to ask if there is a way to automatically do this. My current workflow is really time-taking.