I managed to find a great answer on the AngularJS Google Group, thanks to Pawel Kozlowski.

ng-repeat="item in filtered = (items | filter:filterExpr)"

Would create the filtered list on the fly, you can use filtered.length anywhere else in the current scope to show the count.

Solution

Try this :

HTML

<span ng-bind="nb"></span>

Javascript

$scope.nb = $filter('filter')(items, filterExpr).length;

Documentation

In HTML Template Binding

{{ filter_expression | filter : array : expression : comparator}}

In JavaScript

$filter('filter')(array, expression, comparator)