How to space the thumbs out evenly?

At the base of each post, I have 2 rows of 3 images, but they are not each taking up say 33% of the width. I have applied the following CSS to my posts, which helps but is not perfect. The title does not span the full width of each ‘link’.

.crp_related ul li {

border: 1px solid black;
width: CALC(33% – 22px);

}

a.crp_link {

margin: 0;
left: 0;
right: 0;

}

.crp_title {

display: inline-block;
width: 100% !important;
border: 1px solid black;
margin: auto;
max-width: 100% !important;

}

How do I make the thumbs span around a third each, and have the caption span the length of each thumb please?