// Customize mce editor font sizes
if ( ! function_exists( 'wpex_mce_text_sizes' ) ) {
    function wpex_mce_text_sizes( $initArray ){
        $initArray['fontsize_formats'] = "9px 10px 12px 13px 14px 16px 18px 20px 21px 22px 23px 24px 25px 26px 27px 28px 29px 30px 31px 32px 33px 34px 35px 36px 37px 38px 39px 40px 42px 44px 46px 48px 50px";
        return $initArray;
    }
}
add_filter( 'tiny_mce_before_init', 'wpex_mce_text_sizes' );