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Joomla 'Allowed memory size exhausted' (PHP memory_limit): How to Fix

Symptoms: Fatal error: Allowed memory size of 134217728 bytes exhausted · Often hits while installing an extension, updating, or backing up · Blank page or partial page where the error appears

Mostly verified. This is PHP-engine behaviour, not Joomla-version-specific. Researched 2026-06-01. ✅ Confirmed on our Joomla 5.4.6 test instance: PHP ships with memory_limit = 128M by default — which matches the 134217728 bytes in the classic error.

The error reads:

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate N bytes)

134217728 bytes = exactly 128 MB, the common PHP default. It means a script needed more memory than your memory_limit allows. In Joomla this usually fires while installing a large extension, running an update, or taking a backup.

Common byte values you’ll see: 67108864 = 64M, 134217728 = 128M, 268435456 = 256M, 536870912 = 512M.

How to raise memory_limit (use a method your host supports)

There’s no single universal method — it depends on your hosting. Try these, in order of how commonly they work:

  1. Hosting control panel — most shared hosts (cPanel “MultiPHP INI Editor”, Plesk PHP settings) let you set memory_limit in a UI. Easiest and most reliable.
  2. php.ini — if you control it, set memory_limit = 256M.
  3. .user.ini — on many FastCGI/PHP-FPM hosts, a .user.ini in your site root with memory_limit = 256M works where php.ini isn’t editable.
  4. Ask your host — if none of the above is available, support can raise it.

⚠️ A widely-copied tip says to add php_value memory_limit 512M to .htaccess. Avoid it — it only works on mod_php setups and throws a 500 error on the FastCGI/PHP-FPM stacks most modern hosts use. Prefer the methods above.

After changing it, confirm the new value under System → System Information → PHP Information (look at the Local Value, not just Master Value).

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