How do you license Windows Server in virtual machines? In the usual model you do not license the virtual machine but the physical host: all its cores, at least 8 per processor and 16 per server. With Standard, two virtual machines with Windows Server may run on it; for every two further ones you license all cores again. With Datacenter, the number of VMs on the host is unlimited. Which hypervisor runs makes no difference to this.
Quick decision
| Environment | Licensing |
|---|---|
| One host, 1 to 2 VMs with Windows Server | Standard, all cores once |
| One host, 3 to 4 VMs | Standard twice or Datacenter once |
| One host, many VMs | Datacenter |
| Cluster with live migration | license every host for the VMs that can run on it; usually Datacenter |
| VMs with Linux | need no Windows Server license |
| Host with VMware or Proxmox, VMs with Windows Server | as above, the cores of the host are counted |
The basic rules
The rules come from Microsoft’s product terms and licensing guide.
| Rule | Standard | Datacenter |
|---|---|---|
| What is licensed | all physical cores of the host | all physical cores of the host |
| Minimum quantity | 8 per processor, 16 per server | 8 per processor, 16 per server |
| Operating system environments per round of licensing | 2 | unlimited |
| Host installation in addition to 2 VMs | yes, if it only hosts and manages the VMs | yes |
| Additional VMs | license all cores again for every 2 VMs | not needed |
| Containers with Hyper-V isolation | 2 per round of licensing | unlimited |
| Containers without Hyper-V isolation | unlimited | unlimited |
Microsoft speaks of operating system environments (OSEs). An OSE is a running Windows Server instance, physical or virtual.
What “only host and manage” means
Standard allows two OSEs. The installation on the hardware does not count as long as it serves exclusively to run and manage the virtual machines. As soon as the host itself takes on another task, for example as a file server or domain controller, it is one of the two OSEs. Then only one VM remains with one round of licensing.
In practice this means: put all roles into virtual machines and run only Hyper-V and the management tools on the host. The license calculator assumes this split.
Calculating with Standard: stacking
For every further group of two VMs, the host is fully licensed again. Microsoft calls this “stacking”. It is not enough to buy licenses only for the cores of the additional VM.
Host with two processors of 8 cores each (16 core licenses per round of licensing):
| VMs with Windows Server | Rounds of Standard licensing | Core licenses Standard | Core licenses Datacenter |
|---|---|---|---|
| 1 to 2 | 1 | 16 | 16 |
| 3 to 4 | 2 | 32 | 16 |
| 5 to 6 | 3 | 48 | 16 |
| 7 to 8 | 4 | 64 | 16 |
Host with two processors of 12 cores each (24 core licenses per round of licensing):
| VMs with Windows Server | Rounds of Standard licensing | Core licenses Standard | Core licenses Datacenter |
|---|---|---|---|
| 1 to 2 | 1 | 24 | 24 |
| 3 to 4 | 2 | 48 | 24 |
| 9 to 10 | 5 | 120 | 24 |
The license calculator calculates in exactly this way: it divides the number of VMs by two, rounds up and multiplies by the core licenses of the host. Next to it, it shows the Datacenter option and names the number of VMs from which Datacenter gives the smaller total.
Which VMs count
- Only VMs with Windows Server. A VM with Linux or another operating system needs no Windows Server license and does not count toward the two OSEs.
- Test and secondary servers count too. A VM for tests, print services or updates is a full OSE.
- The size of the VM plays no role. Whether a VM has 2 or 16 virtual cores does not change the number of core licenses of the host.
Different hypervisor, same rules
The license is tied to the hardware on which Windows Server runs as a guest. If you run the VMs on VMware, Proxmox or another hypervisor, all physical cores of the host count as well, with the same minimum quantities and the same VM rights. There is then no installation of Windows Server on the hardware; the calculation for the VMs stays the same.
Clusters and live migration
In a cluster, virtual machines can move from one host to another. In the usual model, the license does not move with them: it is assigned to the server. Every host must therefore be licensed at all times for all Windows Server VMs that run on it.
Sample calculation: two hosts, each with two processors of 8 cores each, eight VMs in total. If one host fails, all eight VMs run on the other.
- With Standard: each host needs licenses for eight VMs, i.e. four rounds of licensing of 16 core licenses each. That is 64 core licenses per host, 128 in total.
- With Datacenter: each host needs 16 core licenses, 32 in total.
In a cluster, Datacenter is therefore usually the smaller bill. The license calculator calculates per host: for each host, enter the maximum number of VMs that run on it in the event of a failure.
Licensing per virtual machine
Since October 2022, Microsoft has offered a second way of counting: licensing individual VMs by their virtual cores, with at least 8 core licenses per VM and 16 per customer. According to the product terms, it requires subscription licenses or licenses with active Software Assurance, also for the CALs. For licenses without Software Assurance, the model by physical cores that this page describes applies. For Windows Server 2025 there is also usage-based billing via Azure Arc.
CALs and activation
- CALs: to access any VM with Windows Server, users or devices need CALs. The host that only hosts and manages VMs does not itself require any. For the version of the CAL, the version in the VM counts, see Which CAL version fits which server.
- Activation: a Hyper-V host with Datacenter can activate its virtual machines automatically (Automatic Virtual Machine Activation). A host with Standard cannot; there you activate each VM with its product key.
Typical cases
One host with two processors and four VMs. Two processors of 8 cores each, VMs for domain controller, file server, application and terminal services. Standard: 32 core licenses. Datacenter: 16 core licenses. Compare the totals in the calculator.
Small server with one VM. One processor with 8 cores, one VM for everything. 16 core licenses of Standard. The second permitted VM remains free, for example for separating domain controller and application later.
Host with two Windows VMs and three Linux VMs. Only the two Windows VMs count. One round of Standard licensing is enough.
A fifth VM is added. So far four VMs with two rounds of Standard licensing. The fifth requires a third round of licensing for all cores. Here at the latest, the comparison with Datacenter is worthwhile, see
Windows Server 2025 Standard or Datacenter.
At VivaKeys
- Windows Server 2025 Standard, 16 Core and Standard Core Add-on
- Windows Server 2025 Datacenter and Datacenter Core Add-on
- For older environments: Windows Server 2022 Standard, 16 Core and Windows Server 2022 Datacenter, 16 Core
All offers are in the Windows Server category. The licensing model as a whole is explained in
Licensing Windows Server: cores, VMs, CALs, the client access licenses in
Windows Server CAL: when you need client access licenses.
Frequently asked questions
Do I need a separate Windows Server license for every VM? No. The host is licensed. With Standard, two VMs are covered each time all cores are licensed, with Datacenter any number.
How many VMs may I run with Windows Server Standard? Two per round of licensing. For four VMs you license all cores of the host twice, for six three times.
Do I have to license the host if VMware runs there instead of Hyper-V? Yes. As soon as VMs with Windows Server run on the host, all physical cores of this host must be licensed.
Do virtual cores or physical cores count? In the model without Software Assurance, the physical cores of the host. The number of virtual cores of a VM plays no role here.
Do I need licenses for both hosts in a cluster? Yes. Every host needs licenses for all Windows Server VMs that can run on it, even if they only move there in the event of a failure.
May the host with Standard also be a file server? Then the host counts as one of the two operating system environments, and only one VM remains per round of licensing. Two VMs alongside the host are only allowed if the host exclusively hosts and manages.
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/licensing/guidance/Core-based-licensing-models
- www.microsoft.com/en-us/licensing/product-licensing/windows-server
- learn.microsoft.com/en-us/windows-server/get-started/locks-limits
- learn.microsoft.com/en-us/windows-server/get-started/automatic-vm-activation