JAVASCRIPT

count all elements with class jquery

var numItems = $('.item').length;

get class count in jquery

// Gets the number of elements with class yourClass
var numItems = $('.yourclass').length

count div class in div jquery

<div class="wrapper">
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
</div>
<script>
alert($('.wrapper').children('.item').length)
</script>