How is Windows Server licensed? Windows Server Standard and Datacenter are licensed by the physical processor cores of the server: all cores, at least 8 per processor and at least 16 per server. Standard then allows two virtual machines, Datacenter any number. In addition, every user or device that accesses the server needs a client access license (CAL), and for Remote Desktop sessions an RDS CAL as well.
Quick decision
- One server, up to two virtual machines: Windows Server Standard, all cores licensed once.
- Many virtual machines on one host: Datacenter, all cores licensed once.
- Access by employees: one Windows Server CAL per user (user CAL) or per device (device CAL), in the version of the server or later.
- Working via Remote Desktop: additionally one RDS CAL per user or device.
- Very small environment with one server: check the Essentials edition, which works without CALs.
The Windows Server license calculator works out the quantities for your server: you enter processors, cores, virtual machines, and users and devices.
The three building blocks
| Building block | What for | How it is counted |
|---|---|---|
| Core licenses (Standard or Datacenter) | The right to run Windows Server on the server | per physical core, with minimum quantities |
| Windows Server CAL | The right to access the server | per user or per device |
| RDS CAL | Remote Desktop sessions and hosted desktops | per user or per device, in addition to the Windows Server CAL |
A CAL is not software. It is not installed; it is the access right for a person or a device.
Counting cores: the rules
The rules come from Microsoft’s product terms and licensing guide for Windows Server 2025.
| Rule | Value |
|---|---|
| What is counted | all physical cores of the server |
| Minimum per processor | 8 core licenses |
| Minimum per server | 16 core licenses |
| Sales units | packs of 2 and of 16 core licenses |
| Virtual machines with Standard | 2 each time all cores are fully licensed |
| Virtual machines with Datacenter | unlimited |
Physical cores are counted, not the logical processors created by hyper-threading. Task Manager shows the number of cores under “Performance” for the CPU. The larger of the two minimums applies in each case: a server with one processor and 6 cores needs 16 core licenses, a server with four processors of 4 cores each needs 32.
Sample calculations
| Server | Physical cores | Core licenses for one round of licensing |
|---|---|---|
| 1 processor with 6 cores | 6 | 16 (minimum per server) |
| 1 processor with 16 cores | 16 | 16 |
| 2 processors with 8 cores each | 16 | 16 |
| 2 processors with 12 cores each | 24 | 24 |
| 4 processors with 4 cores each | 16 | 32 (minimum of 8 per processor) |
The license calculator returns the same quantities and splits them into a base license and additional licenses of 2 cores each.
Virtual machines: Standard or Datacenter
The difference between the editions lies mainly in the virtual machines.
- Standard: once all cores are licensed, you may use Windows Server in two operating system environments. In addition, you may run the installation on the hardware if it exclusively hosts and manages the virtual machines.
- More VMs with Standard: for every two additional virtual machines, you license all cores of the server once more. Microsoft calls this “stacking”.
- Datacenter: once all cores are licensed, the number of virtual machines on this server is not limited.
Example: a host with two processors of 8 cores each and four virtual machines needs 32 core licenses with Standard (twice 16) and 16 with Datacenter. The license calculator shows from which number of VMs Datacenter is the smaller bill for your server. The details are in
Licensing Windows Server and virtualization correctly, the feature differences in
Windows Server 2025 Standard or Datacenter.
Client access licenses: CALs
For Standard and Datacenter, every user or device that accesses the server needs a Windows Server CAL. This applies to signing in to the domain just as much as to file shares or print services.
- A user CAL covers one person with any number of devices, a device CAL one device with any number of people. How to weigh the two is explained in User CAL or device CAL.
- A CAL entitles access to servers of the same or an earlier version. For Windows Server 2025 you need version 2025 CALs. More on this in Which CAL version fits which server.
- No CAL is needed when one licensed server accesses another, for publicly accessible web content and for the host that only runs virtual machines. The cases in detail: Windows Server CAL explained.
Remote Desktop: RDS CAL in addition
If employees work in Remote Desktop sessions on the server, one RDS CAL per user or device is added. It does not replace the Windows Server CAL but supplements it. A terminal server for 25 employees therefore needs 25 Windows Server CALs and 25 RDS CALs. Setup, license server and versions are explained in
RDS CAL: licensing Remote Desktop Services.
Typical cases
Office with one server and 12 employees. One processor with 8 cores, two virtual machines (domain controller and file server). You need 16 core licenses of Windows Server Standard and 12 user CALs.
Host with two processors and four VMs. Two processors of 8 cores each. With Standard that is 32 core licenses, with Datacenter 16. On top come the CALs for all users or devices.
Terminal server for 25 employees. One processor with 16 cores: 16 core licenses of Standard, 25 user CALs and 25 RDS user CALs.
Branch office with one small server. Up to 25 users, one processor with at most 10 cores, no terminal services: here
Windows Server 2025 Essentials can be enough.
All guides on Windows Server and CALs
| Question | Guide |
|---|---|
| Which edition? | Windows Server 2025 Standard or Datacenter |
| Which version? | Windows Server 2025 or 2022 |
| What does it cost? | Windows Server license: what the costs are made up of |
| When do I need CALs? | Windows Server CAL: when you need client access licenses |
| User or device? | User CAL or device CAL |
| Which CAL version? | Which CAL version fits which server |
| Remote Desktop? | RDS CAL: licensing Remote Desktop Services |
| Virtual machines? | Licensing Windows Server and virtualization correctly |
| Small business? | Windows Server 2025 Essentials: limits and use |
| What is new? | Windows Server 2025: the most important new features |
| How long are there updates? | Windows Server end of support: all versions |
| Buy an earlier version? | Buying Windows Server 2019 or 2022 today |
At VivaKeys
Server licenses for Windows Server 2025:
- Windows Server 2025 Standard, 16 Core as the base license, plus, for more than 16 cores, the Core Add-on for every 2 further cores
- Windows Server 2025 Datacenter with 16 cores and the Datacenter Core Add-on
Client access licenses:
You will find all versions and editions in the categories
Windows Server and
CALs. The
license calculator gives you the right combination for your server. If you are unsure, send us your starting point (server, cores, users and devices) via the
contact form.
Frequently asked questions
How many cores do I have to license at least for Windows Server? At least 16 core licenses per server and at least 8 per processor. If the server has more physical cores, every core counts.
Is there a calculator for the Windows Server license? Yes. Our
license calculator works out the core licenses, CALs and RDS CALs from processors, cores, virtual machines, users and devices.
Do I have to renew a Windows Server license? According to Microsoft, the classic license is a perpetual license and does not expire. Only the period in which Microsoft supplies the version with updates is limited, see
Windows Server end of support. Besides that, Microsoft offers usage-based billing via Azure Arc for Windows Server 2025.
Do I still need CALs when licensing by cores? Yes. Standard and Datacenter still require a Windows Server CAL for every user or device that accesses the server. The core license only covers running the server.
Do virtual cores or physical cores count? With the usual licensing, the physical cores of the host count. According to Microsoft, licensing individual virtual machines by virtual cores is only available with Software Assurance or as a subscription.
What are the costs of a Windows Server license made up of? The edition, the number of core licenses, the number of CALs and, where applicable, the RDS CALs. The components are explained in
Windows Server license: what the costs are made up of.
Sources
Checked on 2026-11-10 against the publisher’s information:
- www.microsoft.com/licensing/guidance/Windows-Server-2025
- www.microsoft.com/licensing/terms/productoffering/WindowsServerStandardDatacenterEssentials/EAEAS
- www.microsoft.com/en-us/licensing/product-licensing/windows-server
- www.microsoft.com/licensing/guidance/Core-based-licensing-models
- www.microsoft.com/en-us/licensing/product-licensing/client-access-license
- learn.microsoft.com/en-us/windows-server/get-started/windows-server-pay-as-you-go
- learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/rds-client-access-license