To check the version of joomla you are using includes various steps depends upon the version of joomla you are using. So here various steps are given according to the joomla version

Joomla 1.0.x:

• Login to the backend of your site(admin section of joomla).
• Go to information ---> System info. You will get a screen in which information given related to the joomla version. You can check here joomla version here.

Other way:

If you are not able to access backend, the other way is:

• By FTP, go to root ---> includes ----> joomla ---> version.php.
• Here you can see the source code of the page in which joomla version also given which is not mentioned clearly but you get to know you are using 1.0.

Joomla 1.5.x:

• Login to the backend of your site(admin section of joomla).
• Go to Help ---> System info. You will get a screen in which information given related to the joomla version. You can check here joomla version here.

The Joomla! version is also mentioned at the top right of every pages of the backend.

Other way:

If you are not able to access backend, the other way is:

• By FTP, go to root ---> libraries ----> joomla ---> version.php.
• Here you can see the source code of the page in which joomla version also given which is not mentioned clearly but you get to know you are using 1.5.

Joomla 1.6.x:

• Login to the backend of your site(admin section of joomla).
• Go to Site ---> System Information. You will get a screen in which information given related to the joomla version. You can check here joomla version here.

The Joomla! version is also mentioned at the bottom of every pages of the backend.

Other way:

If you are not able to access backend, the other way is:

• By FTP, go to root ---> libraries ----> joomla ---> version.php.
• Here you can see the source code of the page in which joomla version also given which is not mentioned clearly but you get to know you are using 1.6.

Joomla 1.7.x:

• Login to the backend of your site(admin section of joomla).
• Go to Site ---> System Information. You will get a screen in which information given related to the joomla version. You can check here joomla version here.

Other way:

If you are not able to access backend, the other way is:

• By FTP, go to root ---> libraries ----> joomla ---> version.php.
• Here you can see the source code of the page in which joomla version also given which is not mentioned clearly but you get to know you are using 1.7.

Joomla 2.5.x:

• Login to the backend of your site(admin section of joomla).
• Go to Site ---> System Information. You will get a screen in which information given related to the joomla version. You can check here joomla version here.

The Joomla! version is also mentioned at the bottom of every pages of the backend.

Other way:

If you are not able to access backend, the other way is:

• By FTP, go to root ---> libraries ---> cms ---> version ---> version.php.
• Here you can see the source code of the page in which joomla version also given which is not mentioned clearly but you get to know you are using 2.5.

Joomla 3.x.x:

• Login to the backend of your site(admin section of joomla).
• Go to System ---> System Information. You will get a screen in which information given related to the joomla version. You can check here joomla version here.

The Joomla! version is also mentioned at the bottom of every pages of the backend.

Other way:

If you are not able to access backend, the other way is:

• By FTP, go to root ---> libraries ---> cms ---> version ---> version.php.
• Here you can see the source code of the page in which joomla version also given in the line public $RELEASE and public $DEV_LEVEL.