Error MEM · php

Allowed memory size exhausted

Ben Johnson · last verified 2026-08-04

Also seen as: Fatal error: Allowed memory size of N bytes exhausted · PHP out of memory · memory_limit exceeded

What it actually means

PHP gives each request a memory ceiling. When a script asks for more, PHP stops it immediately with a fatal error rather than letting it consume the whole server.

The message names the exact number and the exact line:

Fatal error: Allowed memory size of 268435456 bytes exhausted
(tried to allocate 20480 bytes) in /home/u1234/htdocs/wp-includes/functions.php on line 812

That line number is rarely the culprit. It’s simply where the last small allocation happened to fall. Something earlier consumed the memory; this line was just unlucky. Look at what the request was doing, not at the line named.

If PHP is configured to hide errors you get a blank page instead — the white screen of death is very often this error with display turned off.

Why it happens

Loading a whole result set into an array

SELECT * FROM orders into an array works fine over 500 rows and dies over 500,000. The query didn’t change; the table grew.

This is the most common cause on any site that has been running for a while.

Image processing

A 4000×3000 JPEG is a couple of megabytes on disk and roughly 48 MB in memory once decoded — width × height × 4 bytes per pixel. Resize two at once and you’re near a 256 MB ceiling before your code does anything else.

Phone photos are routinely this big, so a user upload form hits it long before your test images do.

A plugin doing too much at once

Backup, migration and image-optimisation plugins load large amounts of data in one pass. They usually work on a small site and fail as it grows.

An accidental infinite loop or recursion

A loop that appends to an array without terminating will exhaust memory quickly. If the error appeared right after a code change, look there first.

How to fix it

1. Find what actually used the memory

Log usage at a few points rather than guessing:

error_log('before import: ' . round(memory_get_usage(true) / 1048576) . ' MB');
// ... the suspect code ...
error_log('after import: '  . round(memory_get_usage(true) / 1048576) . ' MB');
error_log('peak: '          . round(memory_get_peak_usage(true) / 1048576) . ' MB');

memory_get_peak_usage() is the number that matters — it’s what PHP compares against the limit.

2. Process rows in batches instead of all at once

The fix for most memory errors is to stop holding everything in memory:

// Dies on a large table
$rows = $db->fetchAll('SELECT * FROM orders');
foreach ($rows as $row) { process($row); }

// Constant memory, any table size
$stmt = $pdo->prepare('SELECT * FROM orders');
$stmt->execute();
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    process($row);
}

Fetching one row at a time keeps usage flat no matter how many rows there are.

3. Free large variables as you go

PHP releases memory when nothing references a value any more, but a long-running loop can hold references longer than you expect:

foreach ($files as $file) {
    $image = imagecreatefromjpeg($file);
    // ... work ...
    imagedestroy($image);   // GD memory is not freed by unset() alone
    unset($image);
}

For images specifically, imagedestroy() matters — the underlying buffer isn’t PHP-managed.

4. Raise the limit, if you genuinely need it

This is a last resort, not a first move. If the code needs 300 MB because it’s badly written, raising the limit just moves the failure.

Where it’s legitimate — a one-off import, a large legitimate dataset — try php.ini in your web root:

memory_limit = 256M

Or for WordPress, in wp-config.php above the “stop editing” line:

define('WP_MEMORY_LIMIT', '256M');

On shared hosting the account ceiling is enforced above PHP, so you cannot raise it past what your plan allows — the setting will silently cap.

5. Shrink images before processing them

If you accept uploads, resize on the way in rather than holding full-resolution files in memory later. Cap the accepted dimensions, and reject anything absurd at the door rather than trying to process it.

On CWP specifically

When this means you've outgrown free hosting

Related errors

• 500 500 Internal Server Error
  Something in your application or server configuration crashed, and the server is deliberately withholding the detail from visitors — the real message is in your error log.
• WSOD White screen of death
  PHP hit a fatal error and error display is turned off, so the server sent an empty page instead of a message.
• TIME Maximum execution time exceeded
  A PHP script ran longer than allowed and was stopped — almost always waiting on a slow query or a slow external service.
• 413 413 Payload Too Large
  You tried to upload something bigger than the server accepts, and it rejected the request before reading it all.