Is there option to fit square to artboard size in Illustrator?

I constantly create square background which I should adjust to artboard size.

Almost every time I miss one or two pixels (Retina is good for that), so I looked for one-click feature "click object to artboard size" and didn't find it.

Probably there is a faster way instead of inserting exact parameters of the artboard to the square dimensions?

Illustrator CS6.

Thanks.