Wrap them in another div, which has a width (or min-width) specified.
<div class="parentContainer">
<div class="floater"></div>
<div class="floater"></div>
<div class="floater"></div>
</div>
.parentContainer {
/* The width of the parent needs to be equal to the total width of the children.
Be sure to include margins/padding/borders in the total. */
width: 600px;
overflow: auto;
}
It also helps to have overflow: auto specified on the containing div, to allow its height to match the child floats.