Windows Server 2025 Core Licensing and CALs Explained: How Many Do You Need?
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Windows Server 2025 is not licensed per server or per user. It is licensed per physical core, and every person or device that connects also needs a Client Access License (CAL). This guide explains both parts, with worked examples, so you can work out what to buy.
The Short Answer
- License every physical core in the host server.
- Buy at least 8 core licenses per processor and at least 16 per server.
- Add a CAL for each user or device that accesses the server.
- Remote Desktop access needs RDS CALs on top of standard CALs.
How Core Licensing Works
Count the physical cores in your server. Hyper-threading does not add cores, so a 12-core processor with 24 threads counts as 12. Then apply the two minimums: 8 cores per processor and 16 cores per server. If your server has fewer cores than the minimum, you still license the minimum.
Worked Examples
| Server hardware | Physical cores | Core licenses needed |
|---|---|---|
| 1 processor, 6 cores | 6 | 16 (server minimum) |
| 1 processor, 16 cores | 16 | 16 |
| 2 processors, 8 cores each | 16 | 16 |
| 2 processors, 12 cores each | 24 | 24 |
| 2 processors, 16 cores each | 32 | 32 |
Combining Core Packs
Core licenses are sold in packs, so you build your total from them. For example, 24 cores is three 8-core packs, and 32 cores is four. Our Windows Server 2025 Datacenter 8 Core Pack is made for this. For a ready-made total, see the 24 core Datacenter license.
Standard and Datacenter Core Rules
Both editions use the same core counting. The difference is virtual machines. Standard covers up to two Windows Server virtual machines per licensed host. To run more, you license all the cores again for each extra pair of VMs. Datacenter covers unlimited Windows Server virtual machines on the licensed host. Our guide Windows Server 2025 Datacenter vs Standard helps you choose between them. You can browse the Windows Server 2025 Standard license or the Datacenter license directly.
What Is a CAL?
A Client Access License gives a user or a device the right to access a Windows Server. The server license alone does not cover the people and machines connecting to it. There are two kinds:
- User CAL: assigned to one person, who can connect from any number of devices. Best when employees use several devices.
- Device CAL: assigned to one device, which any number of people can use. Best for shared PCs, kiosks and shift-based teams.
CALs are counted per named user or per device, not per simultaneous connection. You can mix both types on the same server. The CAL version must be the same as or newer than the server version, so a Windows Server 2025 server needs 2025 CALs.
Do I Need Remote Desktop CALs?
Yes, if people connect to Remote Desktop Services to use a hosted desktop or apps. RDS CALs are separate from Windows Server CALs, and each person or device that uses Remote Desktop Services needs both.
A Quick Planning Checklist
- Count the physical cores and processors in each host.
- Apply the 8-per-processor and 16-per-server minimums.
- Choose Standard or Datacenter based on how many VMs the host will run.
- Count the users or devices that will connect and decide between User and Device CALs.
- Add RDS CALs if you use Remote Desktop Services.
Frequently Asked Questions
Do I license virtual cores or physical cores?
For a host server, license its physical cores. This guide covers licensing for your own on-premises hosts.
Are CALs included with the server license?
No. Server licenses and CALs are bought separately, unless a listing says it is a bundle.
Can I buy fewer than 16 core licenses?
No. Sixteen is the minimum for any single server, even if the server has fewer physical cores.
How many CALs do I need for 20 employees?
One User CAL per employee, so 20, or one Device CAL per device they use if devices are shared. Add RDS CALs if they use Remote Desktop.
Licensing terms can change. Confirm the current rules in Microsoft's product terms before you buy, especially for complex or virtualized environments.
Ready to license your server? Browse our Windows Server and CAL licenses.