There are lots of bad ways to do this – on Stack Overflow, you’ll see a bunch of highly-voted answers that are inline elements with inline-block elements inside them (not great). Here’s my take – might fail on older browsers:


#menu {
    text-align: justify;
}
#menu:after {
    content: " ";
    font-size: 0;
    display: inline-block;
    width: 100%;
}
#menu > div {
    display: inline-block;
}

Fiddle