How to Increase File Upload Limit for WordPress on IIS (Up to 3 GB)

How to Increase File Upload Limit for WordPress on IIS (Up to 3 GB)

When hosting WordPress on IIS (Internet Information Services), large file uploads—such as a 2.5 GB backup file—often fail even if PHP and WordPress limits are set correctly. This happens because IIS enforces its own upload restrictions, independent of WordPress.

The good news: on IIS, this issue is fixable at the server level.

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Why Large Uploads Fail on IIS

By default, IIS limits uploads to around 30 MB. When you try to upload a large WordPress file, the request is blocked before PHP or WordPress ever runs.

Where the limit comes from

The restriction exists in multiple IIS-related layers:

• Request Filtering (IIS)

• ASP.NET maxRequestLength

• web.config

• IIS-level security rules

Because of this, increasing limits in:

• wp-config.php

• php.ini

will not work on their own.

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The Correct Way to Fix It on IIS (Works Reliably)

To allow uploads up to 3 GB, you must update both IIS settings and the site’s web.config.

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Step 1: Increase IIS Request Size

1. Open IIS Manager

2. Select your website

3. Open Request Filtering

4. Click Edit Feature Settings…

5. Set Maximum allowed content length (Bytes) to:

3221225472

(This equals 3 GB)

1. Click OK

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Step 2: Update web.config

In your site’s root directory, edit or create a file named web.config and add the following:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.web>
    <!-- 3 GB (value is in KB) -->
    <httpRuntime
      executionTimeout="1800"
      maxRequestLength="3145728" />
  </system.web>

  <system.webServer>
    <security>
      <requestFiltering>
        <!-- 3 GB (value is in BYTES) -->
        <requestLimits maxAllowedContentLength="3221225472" />
      </requestFiltering>
    </security>
  </system.webServer>
</configuration>

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⚠️ Important: Units Matter

This is a common source of errors:

• maxRequestLength → Kilobytes (KB)

• maxAllowedContentLength → Bytes

Using the wrong unit will cause uploads to fail silently.

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Step 3: Restart IIS

Apply the changes by restarting IIS:

Option 1: From IIS Manager

• Restart the website or application pool

Option 2: Command line (Administrator)

iisreset

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Step 4: Confirm PHP Limits (Recommended)

Make sure PHP limits are equal to or higher than IIS limits:

upload_max_filesize = 5120M
post_max_size = 5120M
max_execution_time = 1800
max_input_time = 1800

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Result

After completing these steps:

• ✅ 2.5 GB WordPress uploads work

• ✅ All-in-One WP Migration uploads succeed

• ✅ No WordPress plugin limitations

• ✅ No need to purchase “Unlimited Upload” extensions

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Final Notes

• These changes require IIS access (VPS, dedicated server, or admin privileges).

• On shared Windows hosting, the provider may need to apply these settings.

• If a reverse proxy or firewall is in front of IIS, additional limits may apply.