How to find your absolute path
From Joomla! Documentation
What is the Absolute Path?
The absolute path is the directory location on a server's drive where the Joomla! Website is located.
In Joomla! v.1.0.x the configuration.php file would contain something like the following, however, it can vary depending on your server.
$mosConfig_absolute_path = '/home/joomla/public_html';
To find your absolute path, copy the following code into a text editor such as Notepad++ or TextEdit. Save the file as a .php naming it whatever you want. (For example, myabsolutepath.php.)
Using your FTP client software, transfer the file you have just created to the root folder of your Joomla Website. Open a Web browser and type in www.yourdomain.com/myabsolutepath.php.
<?php $path = getcwd(); echo "Your Absolute Path is: "; echo $path; ?>
IMPORTANT: For security reasons, delete this file as soon as you have ascertained the information you require.
In Joomla! v.1.5 and later, the absolute path is set in the index.php file in the root directory to the constant JPATH_BASE.
define('JPATH_BASE', dirname(__FILE__) );
Use the constant JPATH_BASE. This constant returns the absolute path to your Joomla! installation directory.
<?php echo JPATH_BASE; ?>