$sql = 'SELECT COUNT(sexo) as total_sex, COUNT(id) as total FROM usuarios GROUP BY sexo';

<?php
$driver = 'mysql';
$database = "dbname=CODINGGROUND";
$dsn = "$driver:host=localhost;unix_socket=/home/cg/mysql/mysql.sock;$database";

$username = 'root';
$password = 'root';

try {
   $conn = new PDO($dsn, $username, $password);
   echo "<h2>Database CODINGGROUND Connected<h2>";
}catch(PDOException $e){
   echo "<h1>" . $e->getMessage() . "</h1>";
}
$sql = 'SELECT COUNT(sex) as total_sex,COUNT(id) as total, sex FROM users GROUP BY sex';
$stmt = $conn->prepare($sql);
$stmt->execute();

$TotalRegistros = 0;
$Total['F'] = 0;
$Total['M'] = 0;

echo "<pre>";
$rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
while($row = array_shift($rows)){
    $TotalRegistros = ($TotalRegistros + $row['total']);
    $Total[$row['sex']] = $row['total_sex'];
    echo "Total de " . $row['sex'] . ": " .$row['total_sex'];
    echo "<br>";
}

echo "Registros: " . $TotalRegistros . "<br>";
$PorcentagemMulheres = ( $Total['F'] / $TotalRegistros ) * 100;
$PorcentagemHomens = ( $Total['M'] / $TotalRegistros ) * 100;
echo "Porcentagem de Mulheres: " . number_format( $PorcentagemMulheres, 2 ) . '%' . "<br>";
echo "Porcentagem de Homens: " . number_format( $PorcentagemHomens, 2 ) . '%' . "<br>";
?>