u can use this:

function wpse128538_resize($url, $width, $height = null, $crop = null, $single = true) {

//validate inputs
    if (!$url OR !$width)
        return false;

//define upload path & dir
    $upload_info = wp_upload_dir();
    $upload_dir = $upload_info[\'basedir\'];
    $upload_url = $upload_info[\'baseurl\'];

//check if $img_url is local
    if (strpos($url, $upload_url) === false)
        return false;

//define path of image
    $rel_path = str_replace($upload_url, \'\', $url);
    $img_path = $upload_dir . $rel_path;

//check if img path exists, and is an image indeed
    if (!file_exists($img_path) OR !getimagesize($img_path))
        return false;

//get image info
    $info = pathinfo($img_path);
    $ext = $info[\'extension\'];
    list($orig_w, $orig_h) = getimagesize($img_path);

//get image size after cropping
    $dims = image_resize_dimensions($orig_w, $orig_h, $width, $height, $crop);
    $dst_w = $dims[4];
    $dst_h = $dims[5];

//use this to check if cropped image already exists, so we can return that instead
    $suffix = "{$dst_w}x{$dst_h}";
    $dst_rel_path = str_replace(\'.\' . $ext, \'\', $rel_path);
    $destfilename = "{$upload_dir}{$dst_rel_path}-{$suffix}.{$ext}";

    if (!$dst_h) {
//can\'t resize, so return original url
        $img_url = $url;
        $dst_w = $orig_w;
        $dst_h = $orig_h;
    }
//else check if cache exists
    elseif (file_exists($destfilename) && getimagesize($destfilename)) {
        $img_url = "{$upload_url}{$dst_rel_path}-{$suffix}.{$ext}";
    }
//else, we resize the image and return the new resized image url
    else {

// Note: pre-3.5 fallback check 
        if (function_exists(\'wp_get_image_editor\')) {

            $editor = wp_get_image_editor($img_path);

            if (is_wp_error($editor) || is_wp_error($editor->resize($width, $height, $crop)))
                return false;

            $resized_file = $editor->save();

            if (!is_wp_error($resized_file)) {
                $resized_rel_path = str_replace($upload_dir, \'\', $resized_file[\'path\']);
                $img_url = $upload_url . $resized_rel_path;
            } else {
                return false;
            }
        } else {

            $resized_img_path = image_resize($img_path, $width, $height, $crop);
            if (!is_wp_error($resized_img_path)) {
                $resized_rel_path = str_replace($upload_dir, \'\', $resized_img_path);
                $img_url = $upload_url . $resized_rel_path;
            } else {
                return false;
            }
        }
    }

//return the output
    if ($single) {
//str return
        $image = $img_url;
    } else {
//array return
        $image = array(
            0 => $img_url,
            1 => $dst_w,
            2 => $dst_h
        );
    }

    return $image;
}