How to Dual Boot Windows 11 and Ubuntu | No-Nonsense Setup

Setting up a dual boot of Windows 11 and Ubuntu lets you choose between both operating systems at startup, with Windows installed first on the same drive.

A dual-boot setup gives you access to both operating systems from one machine. To dual boot Windows 11 and Ubuntu, you start with Windows already installed — shrink its partition in Disk Management, leave the freed space unallocated, and let the Ubuntu installer detect and use it. The whole process takes under an hour and doesn’t require reinstalling Windows.

What You Need Before Starting

The hardware requirements are modest. Any UEFI-based PC that runs Windows 11 can handle Ubuntu as a second OS. You need a USB stick with at least 16 GB of capacity for the installer, and roughly 30–100 GB of free space on your Windows drive (80–100 GB is comfortable for regular use). Ubuntu’s desktop installer works on typical PC hardware, and Ubuntu 24.04 LTS is the current long-term-support release most guides reference, though the exact version depends on which ISO you download.

Does Dual Booting Affect Windows 11?

Dual booting leaves your Windows installation untouched as long as you follow the correct steps. Windows stays on its own partition with all files and settings intact. The Ubuntu installer adds a boot menu called GRUB that lets you pick which OS to start, and Windows Boot Manager remains available as an option. The only Windows-side changes are a smaller C: partition and a few settings tweaks — Fast Startup gets disabled, and any active encryption gets suspended temporarily.

The real risks come from skipping preparation. Repartitioning without a backup, ignoring BitLocker, or booting the USB in the wrong mode can cause boot failures or data loss. Each of those problems has a straightforward fix covered in the steps below.

Dual Booting Windows 11 and Ubuntu: The Setup Process

Step 1: Back Up and Disable Encryption

Before touching any partition settings, back up important files to an external drive or cloud service. Partition changes carry a small risk, and a backup turns a potential disaster into a minor inconvenience.

If Windows has BitLocker or device encryption enabled, suspend it before repartitioning. Open the Control Panel, navigate to System and Security > BitLocker Drive Encryption, and select Suspend protection. Write down or save the recovery key somewhere safe — after the Ubuntu installation changes the boot configuration, Windows may prompt for this key on the first reboot. You can re-enable encryption once the dual boot is confirmed working.

Step 2: Turn Off Fast Startup

Windows 11 enables Fast Startup by default. This feature locks the drive during shutdown, which prevents Ubuntu from accessing the Windows partition correctly. Open Control Panel > Power Options > Choose what the power buttons do, click Change settings that are currently unavailable, and uncheck Turn on fast startup. Click Save changes and restart the PC once before proceeding.

Step 3: Shrink the Windows Partition

Right-click the Start button and select Disk Management. Locate the Windows C: partition — it is usually the largest one. Right-click it and choose Shrink Volume. Enter the amount of space you want to free up in megabytes (30 GB = 30720 MB, 80 GB = 81920 MB). Click Shrink.

A block of unallocated space appears next to the C: partition. Do not format it or create a new volume in Windows. The Ubuntu installer needs raw unallocated space to create its own partitions. If you format it in Windows, the installer will not see usable space.

Step 4: Create a Bootable Ubuntu USB

Download the Ubuntu desktop ISO from the official Ubuntu download page. Insert your USB stick — it will be erased during this process, so move any files off it first. Open Rufus or balenaEtcher, select the downloaded ISO file and the USB drive, then start the writing process. Rufus users should leave the default partition scheme set to GPT and target system to UEFI (non CSM). Etcher handles those settings automatically.

Step 5: Boot the Installer in UEFI Mode

Restart the PC and enter the boot menu — this is usually done by pressing F12, F2, Del, or Esc during startup, depending on your motherboard manufacturer. Select the USB drive from the list. Make sure you choose the entry labeled UEFI rather than one labeled Legacy or CSM. Booting in the wrong mode can prevent GRUB from loading later and may leave you with a system that only boots one OS.

If the USB does not appear in the boot menu, enter the firmware setup (BIOS) and check the boot order or disable Secure Boot temporarily — try Secure Boot enabled first, and only disable it if the installer will not start. Ubuntu boots fine with Secure Boot on most modern systems.

Step 6: Install Ubuntu Alongside Windows

The USB boots into the Ubuntu live environment. Click Install Ubuntu and select your language and keyboard layout. When the installer asks about installation type, choose Install Ubuntu alongside Windows Boot Manager if it appears. This option automatically uses the unallocated space you created.

If the automatic option does not appear, select Something else for manual partitioning. Select the unallocated space, click the + button, and create at least two partitions: a swap partition (4–8 GB, type Swap area) and an ext4 partition mounted at / with the remaining space. A separate /home partition is optional but keeps your personal files separate from the system. The LinuxBlog dual-boot guide walks through the manual partitioning layout in detail for anyone who needs the extra visual reference.

Complete the remaining setup steps — time zone, username, password — and let the installer finish. When prompted, remove the USB stick and restart.

Preparation Steps Overview

Step 6: Verify and Test the Boot Menu

When the PC restarts after installation, you should see the GRUB boot menu with entries for Ubuntu and Windows Boot Manager. Select each one to confirm both operating systems start correctly. Windows appears under a label like Windows Boot Manager or Windows 11, depending on how GRUB detected it.

If the system boots straight into Windows without showing GRUB, enter the firmware setup and check the boot order. Move Ubuntu or GRUB above the Windows entry. On some systems, GRUB is listed under Ubuntu in the boot priority list.

If the system boots straight into Ubuntu without a menu, GRUB may be set to boot Ubuntu automatically and hide the menu. Press and hold Shift (on BIOS systems) or tap Esc (on UEFI systems) during startup to force the menu to appear. You can then edit the GRUB config to show the menu by default.

Common Mistakes and How to Fix Them

How Much Space Should You Give Ubuntu?

Ubuntu’s desktop installer requires at least 25 GB of disk space for the system files and basic applications. A 30 GB allocation works for light use — web browsing, document editing, terminal work. For regular software installs, local file storage, and room to breathe, 80–100 GB is the more practical target. If you plan to use Ubuntu as a daily driver alongside Windows, aim for the larger end of that range and consider a separate /home partition so you can upgrade the system without touching your personal files.

Final Checklist: What a Working Dual Boot Looks Like

• GRUB appears at startup with both Ubuntu and Windows Boot Manager listed
• Ubuntu boots to the desktop with full network and graphics support
• Windows 11 boots normally and the C: partition shows the smaller size
• Fast Startup stays disabled in Windows (re-enable it only if you confirm Ubuntu still boots)
• BitLocker or device encryption can be re-enabled once both OSes are confirmed working
• Both operating systems can access their own data and run updates normally