The short answer
Six situations cover almost every version of this question.
| Situation | Covered by one Windows 11 Pro licence? |
|---|---|
| One PC | Yes — one installation, one device, one person at a time |
| A second PC running at the same time | No — the second machine needs its own licence |
| A replacement PC, with the old one retired | Yes — move the licence and remove Windows from the old machine |
| Reinstalling Windows on the same PC | Yes — as often as you like, and it usually reactivates on its own |
| A virtual machine on the same PC | No — a virtual machine counts as a separate device |
| Dual boot, two Windows installations on one PC | No — two installations need two licences |
So if you are buying for a desktop and a laptop, that is two licences. If you are replacing a dying machine, it is one, moved across. And if you are simply rebuilding the PC you already have, you do not need to buy anything at all.
What “one PC” means in Microsoft’s own words
This is not a policy we have interpreted for you. It is written plainly in the Microsoft Software Licence Terms for Windows, and it is worth reading the actual sentence rather than a summary of it:
“The software is licensed, not sold. Under this agreement, we grant you the right to install and run one instance of the software on your device (the licensed device), for use by one person at a time.”
Three things are being counted there, and people usually only notice the first. One instance of Windows. One device. One person at a time. Nothing in that sentence says the device can never change — and for a retail licence, which is what you get when you buy Windows separately from the hardware, it can. The transfer clause is where that is spelled out:
“If you acquired the software as stand-alone software … you may transfer the software to another device that belongs to you … Every time you transfer the software to a new device, you must remove the software from the prior device. You may not transfer the software to share licenses between devices.”
That single passage gives you both halves of the answer. You may move the licence to a new PC. You may not run it on two at once, and the removal from the old machine is not a formality — it is the condition on which the move is permitted. This is what people mean when they say a Windows licence covers one device at a time.
Our Windows 11 Pro listing describes the licence as valid for 1 PC and as transferable between PCs. Those are not contradictory: the first is the count, the second is what happens when that PC is replaced. One licence, one machine at a time, and it comes with you when the hardware changes.
The one case where you cannot move it
If Windows came pre-installed on the computer when you bought it, you have an OEM licence, and the terms are different: it may be transferred “only with the licensed device”. In other words it belongs to that machine and can only change hands with it. That is the practical difference between the two channels, and it is the reason a retail key is worth more to you over time. Our complete guide to Windows licensing covers OEM, retail and volume in full, and if the terminology itself is the sticking point, licence key, product key and activation key untangles those three.
A genuine Windows 11 Pro key, delivered by email, valid for one PC for the life of that machine. No subscription, and UK-based support if activation gives you any trouble.
What actually happens if you try a second PC
Nothing dramatic, and nothing happens to the first computer. You type the key into the second machine, activation runs, and then it stops with an error. The one you will almost certainly see is 0xC004C008.
Microsoft’s explanation of that code is unusually blunt. The key “has already been used on another device, or it’s being used on more devices than the Microsoft Software License Terms allow”, and the remedy Microsoft gives is to “buy a product key for each one of your devices to activate Windows on them”. You may also meet 0xC004C770 or 0x803FA071, which are the same problem wearing different numbers.
The second PC will still install and run Windows. What it will not do is stay activated: you get the desktop watermark, personalisation settings are switched off, and Windows keeps prompting until it is either activated properly or taken off the machine. It is a nuisance rather than a catastrophe, but it is a permanent one.
This same error appears when someone is legitimately transferring a licence to a replacement PC but has not removed Windows from the old one, or the activation servers still have the old machine on file. That is a different problem with a different fix — our guide to transferring a Windows licence to a new PC walks through it step by step.
Reinstalling, upgrading and changing hardware
Here is the reassuring part, and it is the question most people are really asking underneath the one they typed: reinstalling Windows on the same PC does not use anything up. There is no counter ticking down, no fixed number of activations, no penalty for wiping the machine and starting again. If your licence is linked to a Microsoft account, Microsoft says you “can reinstall the same edition of Windows 11 on this device without entering a product key”, and Windows “will automatically activate online after the installation is complete”. Keep the key somewhere safe anyway — if you have mislaid it, you can recover it from the machine itself before you wipe it.
Changing hardware is where it gets more delicate. Swapping a drive, adding memory or fitting a new graphics card changes nothing. Replacing the motherboard is another matter: to Microsoft’s activation servers that is effectively a different computer, and as Microsoft puts it, “Windows will no longer find a license that matches your device, and you’ll need to reactivate Windows”.
That is recoverable, and the recovery is much easier if you have linked your licence to a Microsoft account beforehand. The activation troubleshooter shows you a list of your devices and asks you to tick “This is the device I’m using right now” — which tells you plainly how Microsoft thinks about all of this. The licence is tracked against a machine, and you are telling it which machine that is now.
If you have done this before, you may remember ringing an automated line and reading out a long installation ID. That service moved online on 3 December 2025. We covered the change and the portal that replaced it in our guide to activating without an internet connection.
Virtual machines, dual boot and other edge cases
These come up constantly and are answered almost nowhere, so here is what the licence terms actually say:
“This license allows you to install only one instance of the software for use on one device, whether that device is physical or virtual. If you want to use the software on more than one virtual device, you must obtain a separate license for each instance.”
Which settles three questions at once.
These are all fine
- Reinstalling on the same PC, any number of times
- Replacing the hard drive, memory or graphics card
- Moving the licence to a replacement PC
- Upgrading that PC from Home to Pro
Each of these is a device
- A virtual machine, even on a PC you already licensed
- A second Windows installation in a dual-boot setup
- A second physical PC, however lightly used
- A test or spare machine kept alongside the main one
The virtual machine one surprises people, because the VM is running on hardware they have already paid to license. Microsoft counts instances, not boxes: Windows 11 Pro includes Hyper-V so you can create the virtual machine, but the Windows running inside it needs a licence of its own. The same logic applies to dual boot — two installations, two instances, two licences — even though only one of them can be running at any moment.
If you need more than one
For most people reading this, the answer is simply one more key. Two machines, two licences, and each one stays with its machine. That is the arrangement Microsoft describes and it is the one we sell: a genuine Windows 11 Pro licence per PC, delivered by email, with no subscription attached to it.
Past a handful of machines the question changes shape. A business kitting out ten or twenty PCs is no longer counting keys one at a time — it is deciding how to image, deploy and manage them, and the licensing choice follows from that rather than the other way round. Our guide to deploying Windows 11 across multiple PCs covers that properly, and if you are weighing up what a small UK business actually needs from Windows, we have written that up too. If you would rather just ask, our support line is UK-based and answers seven days a week.
Frequently asked questions
No. One licence covers one device at a time. The second computer will install Windows but will fail activation with error 0xC004C008, and it will stay unactivated until it has a licence of its own.
Yes, if it is a retail licence bought separately from the hardware. Microsoft’s terms allow the transfer provided you remove Windows from the old machine first. An OEM licence that came pre-installed cannot be moved.
No. You can reinstall on the same PC as many times as you like. There is no activation limit, and if your licence is linked to a Microsoft account, Windows normally reactivates by itself without you entering the key again.
It means the key has already been used on another device, or on more devices than the licence terms allow. Either the key is being used on a second machine, or a transfer was attempted without removing Windows from the previous one.
Yes. Microsoft’s terms count one instance on one device, physical or virtual, so Windows running inside a virtual machine needs its own licence — even when the host PC is already licensed.
Not at the same time. Two machines in regular use need two licences. You could move a single licence between them, but only by removing Windows from one before activating the other, which is not a practical arrangement.
Windows keeps working, but with a watermark on the desktop, personalisation options disabled and recurring prompts to activate. Nothing is deleted and your files are unaffected, but the reminders do not go away on their own.
Five — one per machine. At that scale individual retail keys are still the simplest route. Past roughly twenty machines it is worth looking at volume licensing alongside how you plan to deploy and manage them.
Gary Walsh is the Head of Tech Support at Software Supplies, with more than 20 years in the IT industry. Fully Microsoft-certified and experienced across the full business software stack — from Windows and Office to cloud infrastructure and device management — Gary delivers practical, no-nonsense advice that helps users and businesses get the most from their technology.
