function getItems(url) {
        return $.ajax({
            url: _spPageContextInfo.webAbsoluteUrl + url,
            type: "GET",
            headers: {
                "accept": "application/json;odata=verbose",
            }
        });
    }

getItems( "/_api/Web/Lists/GetByTitle('<list title>')/Items" ).done(function(data){

    var numofItems = data.d.results.length;
     $("#<div id>").append("<b>" + numofItems + "</b>");
});