Licences
Which Windows Server licence and how many CALs you need
A Windows server needs two kinds of licence: a server licence, calculated on the processor's cores (at least 8 per processor and 16 per server), and a client access licence (CAL) for every person or device that uses the server. If people work on the server through Remote Desktop, each of them also needs an RDS CAL.
Two licences, not one
The most common surprise with Windows Server: the server licence does not cover the people who use it. You need two things:
- The server licence, which gives you the right to run Windows Server on a physical machine. It is calculated on the processor's cores.
- Client access licences (CALs), which give people or devices the right to use the server: open files in shared folders, sign in to the domain, print to the network printer.
The rules below come from Microsoft's licensing terms for Windows Server 2022 and 2025. In borderline cases, Microsoft's current terms have the final word.
How to count cores
Three rules, in this order:
- License every physical core in the server. Virtual cores and threads (hyper-threading) do not count.
- At least 8 cores per processor, even if the processor has fewer.
- At least 16 cores per server, even if the server has a single small processor.
Core licences are sold in 2-core and 16-core packs.
| Your server | Cores to license | Packs |
|---|---|---|
| 1 processor, 6 cores | 16 (the per-server minimum applies) | 1 × 16-core or 8 × 2-core |
| 1 processor, 16 cores | 16 | 1 × 16-core |
| 2 processors, 6 cores each | 16 (8 per processor minimum × 2) | 1 × 16-core |
| 2 processors, 12 cores each | 24 | 1 × 16-core + 4 × 2-core |
| 1 processor, 24 cores | 24 | 1 × 16-core + 4 × 2-core |
You can see the core count in Task Manager, on the “Performance” tab under “Cores”, or in the manufacturer's server specification.
Standard, Datacenter or Essentials
The difference between editions is about how many virtual machines you run on the same physical server.
| Edition | What it allows | Who it suits |
|---|---|---|
| Standard | Two virtual machines running Windows Server when all cores are licensed. For two more, you license all the cores again | Most small companies: one physical server, one or two virtual machines |
| Datacenter | Unlimited virtual machines running Windows Server on the licensed server | Servers with many virtual machines, clusters |
| Essentials | One small server, for up to 25 users and 50 devices, with no CALs | Very small companies. Usually supplied with the server by its manufacturer |
Choosing between Standard and Datacenter. Count the Windows Server virtual machines you will run on the server over the next 3–5 years. Each additional pair needs another Standard licence for all cores. Beyond a certain number of machines, Datacenter works out cheaper; we calculate that threshold at current prices, for your server.
Which version. Take the newest version your applications support. Microsoft support ends on 12 January 2027 for Windows Server 2016, on 9 January 2029 for 2019 and on 14 October 2031 for 2022.
CALs: per user or per device
Every person or device that uses the server needs a CAL. Choose whichever type works out better for you:
| Type | Covers | Choose it when |
|---|---|---|
| User CAL | One person, from any number of devices | People work from a desktop, a laptop and a phone |
| Device CAL | One device, however many people use it | Shift work: three people take turns on the same computer |
You can mix both types in the same company, for example User CALs for the office and Device CALs for the warehouse computers.
Three rules companies often overlook:
- The CAL version must be the same as the server version or newer. A 2019 CAL does not give access to a 2022 or 2025 server.
- You count people, not simultaneous connections. 25 employees who use the server, even rarely, means 25 User CALs.
- You do not need a CAL for anonymous access without sign-in (for example, a public website hosted on the server), or for up to two administrators who connect only to administer the server.
If people outside the company (clients, partners) sign in to the server, you can buy an External Connector licence for the server instead of CALs for them. It is only worth it when there are many external users.
Remote Desktop: RDS CALs
If people work on the server through Remote Desktop (for example, 1C or another program runs on the server and everyone connects to it), each of them needs an RDS CAL as well as the standard CAL. Here too, you choose between User and Device.
Exception: two Remote Desktop connections for administration are included and do not need RDS CALs.
A full worked example
A distribution company with 25 employees. It has one physical server with a single 12-core processor. Two virtual machines run on it: one for the domain and file sharing, one for the accounting software. 8 people use the accounting software through Remote Desktop.
| What | How many | Why |
|---|---|---|
| Windows Server Standard, core licences | 16 cores | 12 physical cores, but the per-server minimum is 16. Standard covers both virtual machines |
| Windows Server User CALs | 25 | every employee signs in to the domain and uses the shared folders |
| RDS User CALs | 8 | only the 8 people working through Remote Desktop |
If, a year later, the company adds a third and fourth virtual machine, it buys another 16 Standard cores. The CALs stay the same.
Common mistakes
- Buying the server licence and forgetting the CALs.
- Licensing 12 cores for a 12-core processor, forgetting the 16-core minimum per server.
- Buying CALs for an older version than the server.
- Counting only the people connected at the same time, rather than everyone who uses the server.
- Forgetting RDS CALs for the people who work through Remote Desktop.
What to send us for a quote
For an accurate quote, five answers are enough:
- How many processors does the server have, and how many cores does each have?
- How many Windows Server virtual machines will run on it?
- How many people (or devices) use the server?
- How many of them work through Remote Desktop?
- Which version do you want: 2022 or 2025?
Put them in the “Note” field of the quote request, for example: “16 cores Standard, 25 User CALs, 8 RDS User CALs, 2025”. We send the quote within 4 working hours, with the unit price and the delivery time.
Questions
I have an old server running Windows Server 2016. Can I keep my old CALs if I move to 2025?
No. CALs must be the same version as the server or newer. When you move to 2025, you need 2025 CALs.
My server has hyper-threading and Windows shows 24 logical processors. Do I license 24?
No. Only physical cores count. If the processor has 12 physical cores, hyper-threading shows 24 logical processors, but you license 12, and the per-server minimum brings that up to 16.
Do I need a CAL for the network printer or a security camera?
CALs relate to the people or devices that access the server's services. A device with no user that only receives data from the server is not a typical case; describe it to us and we will tell you what Microsoft's terms require.
Can I move the licence to another server?
Perpetual core licences are tied to the physical server you assigned them to, and moving them is restricted by Microsoft's terms. Ask us before you replace the server.
This guide is general information, accurate on the date it was updated. Manufacturers' prices and rules change, so check them before you decide.