Netmask Calculator
Netmask calculator works out CIDR notation and Network address from IP address, Prefix length (/n) and Subnet mask. The default figures on this page give CIDR notation of 192.168.1.0/24; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
4 steps
- Mask /24 = 255.255.255.0 (11111111.11111111.11111111.00000000)
- Network = address AND mask = 192.168.1.0
- Broadcast = network OR wildcard = 192.168.1.255
- Usable hosts = 2^(32-24) - 2 = 254
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
What the netmask calculator calculates
Derives network address, broadcast, usable host range, mask, wildcard and subnet division for an IPv4 address and prefix.
How to use this netmask calculator
Enter IP address, Prefix length (/n), Subnet mask and Divide into equal subnets. CIDR notation updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind CIDR notation, Network address and Broadcast address.
The method follows RFC 4632, Classless Inter-domain Routing (CIDR), RFC 1878, Variable Length Subnet Table For IPv4, RFC 3021, Using 31-Bit Prefixes on IPv4 Point-to-Point Links and RFC 1918, Address Allocation for Private Internets.
192.168.1.10/24 standard class C network example
With IP address: 192.168.1.10, Prefix length (/n): 24, the calculator returns Network address: 192.168.1.0, Broadcast address: 192.168.1.255, First usable host: 192.168.1.1. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects CIDR notation, Network address and Broadcast address. The inputs you can vary are IP address, Prefix length (/n), Subnet mask, Divide into equal subnets, Hosts needed per subnet and List the resulting subnets.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate my subnet mask?
Derives network address, broadcast, usable host range, mask, wildcard and subnet division for an IPv4 address and prefix. Open “How this is worked out” beside the result to see each step for your own figures.
What does a subnet mask of 255.255. 255.0 mean?
Derives network address, broadcast, usable host range, mask, wildcard and subnet division for an IPv4 address and prefix. On this page it is computed from IP address, Prefix length (/n) and Subnet mask and shown as CIDR notation, Network address and Broadcast address.
How do I find out my netmask?
It needs IP address, Prefix length (/n), Subnet mask, Divide into equal subnets, Hosts needed per subnet and List the resulting subnets. Nothing else is required, and the figures stay in your browser.
What is the IP address range for a /24 subnet?
On the figures this page opens with, the CIDR notation is 192.168.1.0/24. No single number fits everyone: it follows IP address, Prefix length (/n) and Subnet mask, so enter your own above and the answer updates as you type.
What information do I need for the netmask calculator?
You need IP address, Prefix length (/n), Subnet mask, Divide into equal subnets, Hosts needed per subnet and List the resulting subnets. The page opens with default figures that give CIDR notation of 192.168.1.0/24, so you can see the scale before entering your own.
What does this netmask calculator show?
It shows CIDR notation, Network address, Broadcast address, First usable host, Last usable host, Subnet mask, Wildcard mask and Prefix length, with the working and any warnings for your entries.