Css horizontal menu

I have found many sites with code for horizontal drop down pop out out menus with fixes for ie hover, everything works great. I can not however, figure out how to make variable length boxes for the ul items. Has anyone over come this issue? Here is the cookie cutter code for static length elemets :

#menuh ul
{
list-style:none;
margin:0;
padding:0;
float:left;
width:8em; /* width of all menu boxes */
}

I have tried

#7 { width: 7;} and similar schemes with <ul id="7">

but to no avail.

Thx for any help