min-width

min-width sets a lower bound on physical width. It constrains width and can override a conflicting max-width. It does not mean “stop expanding.”

A minimum larger than width

The box declares width:80px and min-width:160px. The minimum wins, so its border box is 160px with this box-sizing rule.

<div class="box">Minimum: 160px</div>

.box {
  box-sizing: border-box;
  width: 80px;
  min-width: 160px;
  padding: 1rem;
  background: #dbeafe;
}

Let a flex item wrap

A flex item’s automatic minimum can preserve an unbroken string’s intrinsic width. The explicit zero allows this item to shrink; overflow-wrap then gives the text a way to wrap.

<div class="row">
  <div class="content">averylongregistrationidentifierwithoutspaces</div>
  <span class="badge">New</span>
</div>

.row {
  display: flex;
  gap: 0.5rem;
  max-width: 18rem;
  border: 1px solid #94a3b8;
}
.content {
  flex: 1;
  min-width: 0;
  overflow-wrap: anywhere;
  background: #eff6ff;
}
.badge {
  flex: 0 0 auto;
}

Automatic minimums and values

The initial value is auto and min-width is not inherited. In ordinary block layout, auto usually resolves to zero. Flex and Grid automatic minimums can depend on content, specified sizes, aspect ratios, scroll-container status, and grid-track spanning. Do not describe auto as universally “no clamp.”

Lengths, percentages of the containing block’s width, and intrinsic values are useful. Zero is an explicit minimum, not a command to hide overflowing content. Negative minimum widths are invalid; newer stretch or sizing functions need separate support checks.

Why a layout still overflows

Min-width:0 allows shrinking but does not wrap an unbreakable child automatically. Pair it with suitable wrapping or scrolling. A large fixed minimum can force horizontal scrolling on mobile. Learn flex-shrink, overflow-wrap, and max-width for the surrounding constraints.

Sources and browser support

MDN: min-width describes the syntax and links to the specification and compatibility data. Check individual values in that table when supporting older browsers.