The following article is technical in nature so if you don't feel comfortable making changes to files via (s)FTP, or from your hosting control panel, you should contact your web hosting provider for assistance.
When talking about a memory limit we're referring to PHP's maximum allowed memory per process. That just means the amount of resources your website is allowed to use while processing a request – or in our case, generating a PDF. When we talk about WordPress's maximum memory limit we're really referring to PHP's maximum memory limit.
It's worth explicitly stating that WordPress memory is different to server memory. Your VPS may have 4GB of memory, but WordPress and your web server are only allocated a small portion of this.
Below are ways you can try increase your memory limit. Their effectiveness will depend entirely on your hosting provider.
You can try change your WP Memory directly in PHP. Edit your WordPress
wp-config.php file and add the following before the
/* That's all, stop editing! Happy blogging. */ line:
define('WP_MEMORY_LIMIT', '128M'); /* change this to a higher value like 256MB or 512MB if needed */
More details about the
WP_MEMORY_LIMIT constant can be found in the WordPress documentation.
wp-config.php method didn't work for you and you have access to your
php.ini file, try change the
memory_limit line to the following:
memory_limit = 128M;
A lot of shared and managed hosting don't allow you to edit the main
php.ini file, but some do allow you to upload your own version which overrides these parameters. Check your web hosting provider's documentation to see if they support this.
If none of the above two options work you can try change the memory limit using the
.htaccess file. Be aware that if this doesn't work it may cause a 500 Internal Server Error (remove the line if this happens).
php_value memory_limit 128M
Contact Hosting Provider
If none of the methods above work for you then get in touch with your web hosting provider and ask them for assistance.