Why Can't I Extend a C Drive With Free Space? How to Fix It?

It's troublesome that I have enough free space on my hard drive, but I can't use them to increase the size of my C drive. I tried Disk Management, and the extend volume option is greyed out. I want to know why this is happening and How I can fix this issue.

Have you ever encountered an "Extend Volume greyed out and can't extend partition" problem? In this post, I will explain why this would happen and teach you how to deal with it. Check out and learn the solution to enable the C drive extension now. Regarding the reason why you can't extend the C drive even with free space, I will discuss the following primary causes:

• The C drive is locked by another process or application, leaving you unable to resize the system partition.
• The unallocated or free space is not behind the C drive you intend to extend. 

Now that we know why you can't resize the C drive with free space. For the first reason, you'd better close all running programs before conducting any actions on the C drive. And for the second reason, you need to turn to a professional and free partition tool EaseUS Partition Master. It can offer two practical tools that enable you to extend the C drive without adjacent unallocated space smoothly and quickly. In addition, this software is operable even if you are a computer beginner.

Solution 1. Allocate Space

This feature will extend your C drive by allocating space from other partitions. You can learn how to use it below:

Solution 2. Adjust with 1-Click

If your C drive is full and receives a warning message for low disk space, "Adjust with 1-Click" of EaseUS Partition Master would be your best solution. Here is the complete guide on extending the C drive with "Adjust with 1-Click":

If you only have one partition(C drive) on your hard drive, you can explore the method for extending the C drive from another disk in the following article:

Related Article: How to Extend C Drive from Another Disk in Windows 10/11?