Unordered List as boxes?

I changed my li’s padding to em’s, but the width and height now need to be different number, so you never know if you have a true square…

I also tried increasing the font from 1em to 1.2em and that really messed up my original width and height.

Isn’t there a more uniform/calculated way to do this?

(The borders look funky in this screenshot, but are fine on my computer.)