Untitled

body {
  width:1024px;
  margin:0 auto;
}

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>my site</title>
</head>

<body>

<div class="set-width"></div>

</body>
</html>

set-width {    width:1024px;
margin:0 auto;}

<div class="navbar-fixed">
  <nav>
    <div class="nav-wrapper white"><div class="set-width">
      <a href="#" class="brand-logo center"><h5 class="center-align"><img src="Logo.png"></h5></a>
      <ul id="nav-mobile" class="left hide-on-med-and-down">
        <li><a href="conta.html"><h5 class="center-align"><img class="responsive-img" src="http://feely.com.br/teste/Avatar.png"></h5></a></li>
        <li><a href="conta.html"></h5><span class="grey-text text-darken-4">OLÁ, USUÁRIO!</span></a></li>
      </ul>
      <ul id="nav-mobile" class="right hide-on-med-and-down">
        <li><a href="carrinho.html"><span class="grey-text text-darken-4"><i class="material-icons">shopping_cart</i></span></a></li>
        <li><a href="buscar.html"><span class="grey-text text-darken-4"><i class="material-icons">search</i></span></a></li></div>
        </ul>
    </div>
  </nav>
 </div>