Horizontal Menu

[degadesign]

Hello.
I have a horizontal menu with submenus also horizontally, the problem is that I would like to divide the menu items automatically in 100% of the available space and I can't understand how.

ES.
item 1
item 2
item 3
item 3a
item 3b
item 4
item 5
item 5a
item 5b
item 5c
item 5d

I used

selector ul.sub-menu {
max-width: 100% !important;
right: 0px;
position: fixed;
}

selector ul.sub-menu li.menu-item {
width: 25%;
margin:auto;
float: left;
text-align: center;
}

selector ul.sub-menu li.menu-item a {
display: block;
}

}

the 4 items of the submenu of item 5 are positioned correctly dividing themselves into 100% of the available space
instead the 2 items of the submenu of item 3 occupy only 50% of the available space, instead each of these items should occupy 50%

I am using Navigation Menu.

I thank in advance those who can help me.