Functions used to convert 64bit Steam ID to 32bit and the other way around.

steamid_conversion.php

<?php

function convert_steamid_64bit_to_32bit($id)
{
  $result = substr($id, 3) - 61197960265728;
  return (string) $result;
}

function convert_steamid_32bit_to_64bit($id)
{
  $result = '765'.($id + 61197960265728);
  return (string) $result;
}

$sixtyfour = '76561197992765754';
$thirtytwo = '32500026';

var_dump(convert_steamid_32bit_to_64bit($thirtytwo) === $sixtyfour); // bool(true)
var_dump(convert_steamid_64bit_to_32bit($sixtyfour) === $thirtytwo); // bool(true)

Would you happen to know a direct relation for Group ID as well?

Thanks! you saved much time for me